diff --git a/src/ApplicationFactory.php b/src/ApplicationFactory.php
index 4ef346a..5201817 100644
--- a/src/ApplicationFactory.php
+++ b/src/ApplicationFactory.php
@@ -1,11 +1,14 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 use PHPFastCGI\FastCGIDaemon\Command\DaemonRunCommand;
 use PHPFastCGI\FastCGIDaemon\Driver\DriverContainer;
 use PHPFastCGI\FastCGIDaemon\Driver\DriverContainerInterface;
 use Symfony\Component\Console\Application;
+use Symfony\Component\Console\Command\Command;
 
 /**
  * The default implementation of the ApplicationFactoryInterface.
@@ -30,7 +33,7 @@ public function __construct(DriverContainerInterface $driverContainer = null)
     /**
      * {@inheritdoc}
      */
-    public function createApplication($kernel, $commandName = null, $commandDescription = null)
+    public function createApplication($kernel, string $commandName = null, string $commandDescription = null): Application
     {
         $command = $this->createCommand($kernel, $commandName, $commandDescription);
 
@@ -43,7 +46,7 @@ public function createApplication($kernel, $commandName = null, $commandDescript
     /**
      * {@inheritdoc}
      */
-    public function createCommand($kernel, $commandName = null, $commandDescription = null)
+    public function createCommand($kernel, string $commandName = null, string $commandDescription = null): Command
     {
         $kernelObject = $this->getKernelObject($kernel);
 
@@ -60,7 +63,7 @@ public function createCommand($kernel, $commandName = null, $commandDescription
      *
      * @return KernelInterface The kernel as an object implementing the KernelInterface
      */
-    private function getKernelObject($kernel)
+    private function getKernelObject($kernel): KernelInterface
     {
         if ($kernel instanceof KernelInterface) {
             return $kernel;
diff --git a/src/ApplicationFactoryInterface.php b/src/ApplicationFactoryInterface.php
index 3cb5933..f25c54e 100644
--- a/src/ApplicationFactoryInterface.php
+++ b/src/ApplicationFactoryInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 use Symfony\Component\Console\Application;
@@ -20,7 +22,7 @@ interface ApplicationFactoryInterface
      *
      * @return Application The Symfony console application
      */
-    public function createApplication($kernel, $commandName = null, $commandDescription = null);
+    public function createApplication($kernel, string $commandName = null, string $commandDescription = null): Application;
 
     /**
      * Create a Symfony console command.
@@ -31,5 +33,5 @@ public function createApplication($kernel, $commandName = null, $commandDescript
      *
      * @return Command The Symfony console command
      */
-    public function createCommand($kernel, $commandName = null, $commandDescription = null);
+    public function createCommand($kernel, string $commandName = null, string $commandDescription = null): Command;
 }
diff --git a/src/CallbackKernel.php b/src/CallbackKernel.php
index c90b5b8..638e16f 100644
--- a/src/CallbackKernel.php
+++ b/src/CallbackKernel.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 use PHPFastCGI\FastCGIDaemon\Http\RequestInterface;
@@ -22,7 +24,7 @@ final class CallbackKernel implements KernelInterface
      *
      * @throws \InvalidArgumentException When not given callable callback
      */
-    public function __construct($handler)
+    public function __construct(callable $handler)
     {
         if (!is_callable($handler)) {
             throw new \InvalidArgumentException('Handler callback is not callable');
diff --git a/src/Command/DaemonRunCommand.php b/src/Command/DaemonRunCommand.php
index 7ad0c5e..0226c9f 100644
--- a/src/Command/DaemonRunCommand.php
+++ b/src/Command/DaemonRunCommand.php
@@ -1,9 +1,12 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Command;
 
 use PHPFastCGI\FastCGIDaemon\DaemonInterface;
 use PHPFastCGI\FastCGIDaemon\DaemonOptions;
+use PHPFastCGI\FastCGIDaemon\DaemonOptionsInterface;
 use PHPFastCGI\FastCGIDaemon\Driver\DriverContainerInterface;
 use PHPFastCGI\FastCGIDaemon\KernelInterface;
 use Symfony\Component\Console\Command\Command;
@@ -70,9 +73,9 @@ public function __construct(KernelInterface $kernel, DriverContainerInterface $d
      * @param InputInterface  $input  The  Symfony command input
      * @param OutputInterface $output The Symfony command output
      *
-     * @return DaemonOptions The daemon configuration
+     * @return DaemonOptionsInterface The daemon configuration
      */
-    private function getDaemonOptions(InputInterface $input, OutputInterface $output)
+    private function getDaemonOptions(InputInterface $input, OutputInterface $output): DaemonOptionsInterface
     {
         $logger = new ConsoleLogger($output);
 
diff --git a/src/DaemonFactoryInterface.php b/src/DaemonFactoryInterface.php
index 65249ec..001fd74 100644
--- a/src/DaemonFactoryInterface.php
+++ b/src/DaemonFactoryInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 /**
@@ -18,7 +20,7 @@ interface DaemonFactoryInterface
      *
      * @return DaemonInterface The FastCGI daemon
      */
-    public function createDaemon(KernelInterface $kernel, DaemonOptions $options, $fd = DaemonInterface::FCGI_LISTENSOCK_FILENO);
+    public function createDaemon(KernelInterface $kernel, DaemonOptions $options, int $fd = DaemonInterface::FCGI_LISTENSOCK_FILENO): DaemonInterface;
 
     /**
      * Create a FastCGI daemon listening on a given address. The default host is
@@ -31,5 +33,5 @@ public function createDaemon(KernelInterface $kernel, DaemonOptions $options, $f
      *
      * @return DaemonInterface The FastCGI daemon
      */
-    public function createTcpDaemon(KernelInterface $kernel, DaemonOptions $options, $host, $port);
+    public function createTcpDaemon(KernelInterface $kernel, DaemonOptions $options, string $host, int $port): DaemonInterface;
 }
diff --git a/src/DaemonInterface.php b/src/DaemonInterface.php
index dc370f5..e5dec1a 100644
--- a/src/DaemonInterface.php
+++ b/src/DaemonInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 /**
@@ -46,13 +48,13 @@ interface DaemonInterface
      *
      * @throws \Exception On fatal error
      */
-    public function run();
+    public function run(): void;
 
     /**
      * Flag the daemon for shutting down. This will stop it from accepting
      * requests.
-     * 
+     *
      * @param string|null Optional message.
      */
-    public function flagShutdown($message = null);
+    public function flagShutdown(string $message = null): void;
 }
diff --git a/src/DaemonOptions.php b/src/DaemonOptions.php
index 6ade03f..d57403f 100644
--- a/src/DaemonOptions.php
+++ b/src/DaemonOptions.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 use Psr\Log\LoggerInterface;
@@ -19,13 +21,13 @@ final class DaemonOptions implements DaemonOptionsInterface
      * Constructor.
      *
      * The value of the LOGGER option must implement the PSR-3 LoggerInterface.
-     * 
+     *
      * For the REQUEST_LIMIT, MEMORY_LIMIT and TIME_LIMIT options, NO_LIMIT can
      * be used to specify that these metrics should not cause the daemon to
      * shutdown.
      *
      * @param array $options The options to configure the daemon with
-     * 
+     *
      * @throws \InvalidArgumentException On unrecognised option
      */
     public function __construct(array $options = [])
@@ -52,7 +54,7 @@ public function __construct(array $options = [])
         }
     }
 
-    public function getOption($option)
+    public function getOption(string $option)
     {
         if (!isset($this->options[$option])) {
             throw new \InvalidArgumentException('Unknown option: '.$option);
diff --git a/src/DaemonOptionsInterface.php b/src/DaemonOptionsInterface.php
index 7c6dedb..e0cb075 100644
--- a/src/DaemonOptionsInterface.php
+++ b/src/DaemonOptionsInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 interface DaemonOptionsInterface
@@ -22,5 +24,5 @@ interface DaemonOptionsInterface
      *
      * @throws \InvalidArgumentException On unrecognised option
      */
-    public function getOption($option);
+    public function getOption(string $option);
 }
diff --git a/src/DaemonTrait.php b/src/DaemonTrait.php
index e9712e2..e499305 100644
--- a/src/DaemonTrait.php
+++ b/src/DaemonTrait.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 use PHPFastCGI\FastCGIDaemon\Exception\ShutdownException;
@@ -38,10 +40,10 @@ trait DaemonTrait
 
     /**
      * Flags the daemon for shutting down.
-     * 
+     *
      * @param string $message Optional shutdown message
      */
-    public function flagShutdown($message = null)
+    public function flagShutdown(string $message = null): void
     {
         $this->isShutdown = true;
         $this->shutdownMessage = (null === $message ? 'Daemon flagged for shutdown' : $message);
@@ -51,9 +53,9 @@ public function flagShutdown($message = null)
      * Loads to configuration from the daemon options and installs signal
      * handlers.
      *
-     * @param DaemonOptions $daemonOptions
+     * @param DaemonOptionsInterface $daemonOptions
      */
-    private function setupDaemon(DaemonOptions $daemonOptions)
+    private function setupDaemon(DaemonOptionsInterface $daemonOptions): void
     {
         $this->requestCount = 0;
         $this->requestLimit = $daemonOptions->getOption(DaemonOptions::REQUEST_LIMIT);
@@ -74,7 +76,7 @@ private function setupDaemon(DaemonOptions $daemonOptions)
      *
      * @param int[] $statusCodes The status codes of sent responses
      */
-    private function considerStatusCodes($statusCodes)
+    private function considerStatusCodes(array $statusCodes): void
     {
         $this->requestCount += count($statusCodes);
 
@@ -94,7 +96,7 @@ private function considerStatusCodes($statusCodes)
      *
      * @throws ShutdownException On receiving a SIGINT or SIGALRM
      */
-    private function installSignalHandlers()
+    private function installSignalHandlers(): void
     {
         declare (ticks = 1);
 
@@ -114,7 +116,7 @@ private function installSignalHandlers()
      *
      * @throws ShutdownException When limits in the daemon options are exceeded
      */
-    private function checkDaemonLimits()
+    private function checkDaemonLimits(): void
     {
         if ($this->isShutdown) {
             throw new ShutdownException($this->shutdownMessage);
diff --git a/src/Driver/DriverContainer.php b/src/Driver/DriverContainer.php
index a7dfb82..4f06e77 100644
--- a/src/Driver/DriverContainer.php
+++ b/src/Driver/DriverContainer.php
@@ -1,7 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver;
 
+use PHPFastCGI\FastCGIDaemon\DaemonFactoryInterface;
+
 final class DriverContainer implements DriverContainerInterface
 {
     /**
@@ -25,7 +29,7 @@ public function __construct()
     /**
      * {@inheritdoc}
      */
-    public function getFactory($driver)
+    public function getFactory(string $driver): DaemonFactoryInterface
     {
         if (!isset($this->drivers[$driver])) {
             throw new \InvalidArgumentException('Unknown driver: '.$driver);
diff --git a/src/Driver/DriverContainerInterface.php b/src/Driver/DriverContainerInterface.php
index a3168d1..1c216ad 100644
--- a/src/Driver/DriverContainerInterface.php
+++ b/src/Driver/DriverContainerInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver;
 
 use PHPFastCGI\FastCGIDaemon\DaemonFactoryInterface;
@@ -13,5 +15,5 @@ interface DriverContainerInterface
      *
      * @return DaemonFactoryInterface The daemon factory for the driver
      */
-    public function getFactory($driver);
+    public function getFactory(string $driver): DaemonFactoryInterface;
 }
diff --git a/src/Driver/Userland/Connection/ConnectionInterface.php b/src/Driver/Userland/Connection/ConnectionInterface.php
index 4d1640c..8728753 100644
--- a/src/Driver/Userland/Connection/ConnectionInterface.php
+++ b/src/Driver/Userland/Connection/ConnectionInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\Connection;
 
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\Exception\ConnectionException;
@@ -19,7 +21,7 @@ interface ConnectionInterface
      *
      * @throws ConnectionException On failure
      */
-    public function read($length);
+    public function read(int $length): string;
 
     /**
      * Write data to the connection.
@@ -28,17 +30,17 @@ public function read($length);
      *
      * @throws ConnectionException On failure
      */
-    public function write($buffer);
+    public function write(string $buffer): void;
 
     /**
      * Tests to see if the connection has been closed.
      *
      * @return bool True if the connection has been closed, false otherwise
      */
-    public function isClosed();
+    public function isClosed(): bool;
 
     /**
      * Closes the connection it from the pool.
      */
-    public function close();
+    public function close(): void;
 }
diff --git a/src/Driver/Userland/Connection/ConnectionPoolInterface.php b/src/Driver/Userland/Connection/ConnectionPoolInterface.php
index 73d8f8f..df722f4 100644
--- a/src/Driver/Userland/Connection/ConnectionPoolInterface.php
+++ b/src/Driver/Userland/Connection/ConnectionPoolInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\Connection;
 
 /**
@@ -19,25 +21,25 @@ interface ConnectionPoolInterface
      * @param int $timeout Upper bound on the amount of time to wair for readable connections
      *
      * @return ConnectionInterface[]
-     * 
+     *
      * @throws \RuntimeException On encountering fatal error
      */
-    public function getReadableConnections($timeout);
+    public function getReadableConnections(int $timeout): array;
 
     /**
      * Returns the number of active connections in the pool.
      *
      * @return int
      */
-    public function count();
+    public function count(): int;
 
     /**
      * Stop the connection pool from accepting new connections.
      */
-    public function shutdown();
+    public function shutdown(): void;
 
     /**
      * Close the connection pool and free any associated resources.
      */
-    public function close();
+    public function close(): void;
 }
diff --git a/src/Driver/Userland/Connection/StreamSocketConnection.php b/src/Driver/Userland/Connection/StreamSocketConnection.php
index 19f9aad..2330161 100644
--- a/src/Driver/Userland/Connection/StreamSocketConnection.php
+++ b/src/Driver/Userland/Connection/StreamSocketConnection.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\Connection;
 
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\Exception\ConnectionException;
@@ -39,7 +41,7 @@ public function __construct($socket)
      *
      * @return ConnectionException
      */
-    protected function createExceptionFromLastError($function)
+    protected function createExceptionFromLastError(string $function): ConnectionException
     {
         $this->close();
 
@@ -49,7 +51,7 @@ protected function createExceptionFromLastError($function)
     /**
      * {@inheritdoc}
      */
-    public function read($length)
+    public function read(int $length): string
     {
         if ($this->isClosed()) {
             throw new ConnectionException('Connection has been closed');
@@ -71,7 +73,7 @@ public function read($length)
     /**
      * {@inheritdoc}
      */
-    public function write($buffer)
+    public function write(string $buffer): void
     {
         if ($this->isClosed()) {
             throw new ConnectionException('Connection has been closed');
@@ -85,7 +87,7 @@ public function write($buffer)
     /**
      * {@inheritdoc}
      */
-    public function isClosed()
+    public function isClosed(): bool
     {
         return $this->closed;
     }
@@ -93,7 +95,7 @@ public function isClosed()
     /**
      * {@inheritdoc}
      */
-    public function close()
+    public function close(): void
     {
         if (!$this->isClosed()) {
             fclose($this->socket);
diff --git a/src/Driver/Userland/Connection/StreamSocketConnectionPool.php b/src/Driver/Userland/Connection/StreamSocketConnectionPool.php
index 61d4ff9..a872bff 100644
--- a/src/Driver/Userland/Connection/StreamSocketConnectionPool.php
+++ b/src/Driver/Userland/Connection/StreamSocketConnectionPool.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\Connection;
 
 /**
@@ -19,7 +21,7 @@ final class StreamSocketConnectionPool implements ConnectionPoolInterface
     private $clientSockets;
 
     /**
-     * @var Connection[]
+     * @var ConnectionInterface[]
      */
     private $connections;
 
@@ -35,7 +37,7 @@ final class StreamSocketConnectionPool implements ConnectionPoolInterface
      */
     public function __construct($socket)
     {
-        stream_set_blocking($socket, 0);
+        stream_set_blocking($socket, false);
 
         $this->serverSocket  = $socket;
         $this->clientSockets = [];
@@ -47,7 +49,7 @@ public function __construct($socket)
     /**
      * {@inheritdoc}
      */
-    public function getReadableConnections($timeout)
+    public function getReadableConnections(int $timeout): array
     {
         $this->removeClosedConnections();
 
@@ -76,7 +78,7 @@ public function getReadableConnections($timeout)
     /**
      * {@inheritdoc}
      */
-    public function count()
+    public function count(): int
     {
         $this->removeClosedConnections();
 
@@ -86,7 +88,7 @@ public function count()
     /**
      * {@inheritdoc}
      */
-    public function shutdown()
+    public function shutdown(): void
     {
         $this->shutdown = true;
     }
@@ -94,7 +96,7 @@ public function shutdown()
     /**
      * {@inheritdoc}
      */
-    public function close()
+    public function close(): void
     {
         $this->removeClosedConnections();
 
@@ -115,7 +117,7 @@ public function close()
      * @param resource[] $readSockets The sockets to test for readability (output parameter)
      * @param int        $timeout     The stream select call timeout
      */
-    private function selectConnections(&$readSockets, $timeout)
+    private function selectConnections(&$readSockets, int $timeout): void
     {
         // stream_select will not always preserve array keys
         // call it with a (deep) copy so the original is preserved
@@ -145,12 +147,12 @@ private function selectConnections(&$readSockets, $timeout)
     /**
      * Accept incoming connections from the server stream socket.
      */
-    private function acceptConnection()
+    private function acceptConnection(): void
     {
         $clientSocket = @stream_socket_accept($this->serverSocket);
 
         if (false !== $clientSocket) {
-            stream_set_blocking($clientSocket, 0);
+            stream_set_blocking($clientSocket, false);
 
             $connection = new StreamSocketConnection($clientSocket);
 
@@ -161,10 +163,7 @@ private function acceptConnection()
         }
     }
 
-    /**
-     * Remove connections.
-     */
-    private function removeClosedConnections()
+    private function removeClosedConnections(): void
     {
         foreach ($this->connections as $id => $connection) {
             if ($connection->isClosed()) {
diff --git a/src/Driver/Userland/ConnectionHandler/ConnectionHandler.php b/src/Driver/Userland/ConnectionHandler/ConnectionHandler.php
index 50b637d..4c4368a 100644
--- a/src/Driver/Userland/ConnectionHandler/ConnectionHandler.php
+++ b/src/Driver/Userland/ConnectionHandler/ConnectionHandler.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\ConnectionHandler;
 
 use PHPFastCGI\FastCGIDaemon\DaemonInterface;
@@ -73,7 +75,7 @@ public function __construct(KernelInterface $kernel, ConnectionInterface $connec
     /**
      * {@inheritdoc}
      */
-    public function ready()
+    public function ready(): array
     {
         try {
             $data = $this->connection->read(self::READ_LENGTH);
@@ -85,10 +87,10 @@ public function ready()
 
             $statusCodes = [];
 
-            while (null !== ($record = $this->readRecord())) {
+            while (!empty($record = $this->readRecord())) {
                 $statusCode = $this->processRecord($record);
 
-                if (null != $statusCode) {
+                if (null !== $statusCode) {
                     $statusCodes[] = $statusCode;
                 }
             }
@@ -104,7 +106,7 @@ public function ready()
     /**
      * {@inheritdoc}
      */
-    public function shutdown()
+    public function shutdown(): void
     {
         $this->shutdown = true;
     }
@@ -112,7 +114,7 @@ public function shutdown()
     /**
      * {@inheritdoc}
      */
-    public function close()
+    public function close(): void
     {
         $this->buffer       = null;
         $this->bufferLength = 0;
@@ -131,7 +133,7 @@ public function close()
     /**
      * {@inheritdoc}
      */
-    public function isClosed()
+    public function isClosed(): bool
     {
         return $this->closed;
     }
@@ -142,13 +144,13 @@ public function isClosed()
     /**
      * Read a record from the connection.
      *
-     * @return array|null The record that has been read
+     * @return array The record that has been read
      */
-    private function readRecord()
+    private function readRecord(): array
     {
         // Not enough data to read header
         if ($this->bufferLength < 8) {
-            return;
+            return [];
         }
 
         $headerData = substr($this->buffer, 0, 8);
@@ -159,7 +161,7 @@ private function readRecord()
 
         // Not enough data to read rest of record
         if ($this->bufferLength - 8 < $record['contentLength'] + $record['paddingLength']) {
-            return;
+            return [];
         }
 
         $record['contentData'] = substr($this->buffer, 8, $record['contentLength']);
@@ -178,11 +180,11 @@ private function readRecord()
      *
      * @param array $record The record that has been read
      *
-     * @return int Number of dispatched requests
+     * @return null|int Number of dispatched requests
      *
      * @throws ProtocolException If the client sends an unexpected record.
      */
-    private function processRecord(array $record)
+    private function processRecord(array $record): ?int
     {
         $requestId = $record['requestId'];
 
@@ -193,7 +195,7 @@ private function processRecord(array $record)
         } elseif (!isset($this->requests[$requestId])) {
             throw new ProtocolException('Invalid request id for record of type: '.$record['type']);
         } elseif (DaemonInterface::FCGI_PARAMS === $record['type']) {
-            while (strlen($content) > 0) {
+            while (null !== $content && strlen($content) > 0) {
                 $this->readNameValuePair($requestId, $content);
             }
         } elseif (DaemonInterface::FCGI_STDIN === $record['type']) {
@@ -216,11 +218,11 @@ private function processRecord(array $record)
      * Process a FCGI_BEGIN_REQUEST record.
      *
      * @param int    $requestId   The request id sending the record
-     * @param string $contentData The content of the record
+     * @param null|string $contentData The content of the record
      *
      * @throws ProtocolException If the FCGI_BEGIN_REQUEST record is unexpected
      */
-    private function processBeginRequestRecord($requestId, $contentData)
+    private function processBeginRequestRecord(int $requestId, ?string $contentData): void
     {
         if (isset($this->requests[$requestId])) {
             throw new ProtocolException('Unexpected FCGI_BEGIN_REQUEST record');
@@ -255,9 +257,9 @@ private function processBeginRequestRecord($requestId, $contentData)
      * Read a FastCGI name-value pair from a buffer and add it to the request params.
      *
      * @param int    $requestId The request id that sent the name-value pair
-     * @param string $buffer    The buffer to read the pair from (pass by reference)
+     * @param null|string $buffer    The buffer to read the pair from (pass by reference)
      */
-    private function readNameValuePair($requestId, &$buffer)
+    private function readNameValuePair(int $requestId, ?string &$buffer): void
     {
         $nameLength  = $this->readFieldLength($buffer);
         $valueLength = $this->readFieldLength($buffer);
@@ -280,7 +282,7 @@ private function readNameValuePair($requestId, &$buffer)
      *
      * @return int The length of the field
      */
-    private function readFieldLength(&$buffer)
+    private function readFieldLength(string &$buffer): int
     {
         $block  = unpack('C4', $buffer);
 
@@ -306,7 +308,7 @@ private function readFieldLength(&$buffer)
      * @param int $appStatus      The application status to declare
      * @param int $protocolStatus The protocol status to declare
      */
-    private function endRequest($requestId, $appStatus = 0, $protocolStatus = DaemonInterface::FCGI_REQUEST_COMPLETE)
+    private function endRequest(int $requestId, int $appStatus = 0, int $protocolStatus = DaemonInterface::FCGI_REQUEST_COMPLETE): void
     {
         $content = pack('NCx3', $appStatus, $protocolStatus);
         $this->writeRecord($requestId, DaemonInterface::FCGI_END_REQUEST, $content);
@@ -329,7 +331,7 @@ private function endRequest($requestId, $appStatus = 0, $protocolStatus = Daemon
      * @param int    $type      The type of record
      * @param string $content   The content of the record
      */
-    private function writeRecord($requestId, $type, $content = null)
+    private function writeRecord(int $requestId, int $type, string $content = null): void
     {
         $contentLength = null === $content ? 0 : strlen($content);
 
@@ -349,7 +351,7 @@ private function writeRecord($requestId, $type, $content = null)
      * @param string   $headerData The header -data to write (including terminating CRLFCRLF)
      * @param resource $stream     The stream to write
      */
-    private function writeResponse($requestId, $headerData, $stream)
+    private function writeResponse(int $requestId, string $headerData, $stream): void
     {
         $data = $headerData;
         $eof  = false;
@@ -380,9 +382,11 @@ private function writeResponse($requestId, $headerData, $stream)
      *
      * @param int $requestId The request id that is ready to dispatch
      *
+     * @return int status code from the response.
+     *
      * @throws \LogicException If the kernel doesn't return a valid response
      */
-    private function dispatchRequest($requestId)
+    private function dispatchRequest(int $requestId): int
     {
         $request = new Request(
             $this->requests[$requestId]['params'],
@@ -415,7 +419,7 @@ private function dispatchRequest($requestId)
      * @param int               $requestId The request id to respond to
      * @param ResponseInterface $response  The PSR-7 HTTP response message
      */
-    private function sendResponse($requestId, ResponseInterface $response)
+    private function sendResponse(int $requestId, ResponseInterface $response): void
     {
         $statusCode   = $response->getStatusCode();
         $reasonPhrase = $response->getReasonPhrase();
@@ -437,7 +441,7 @@ private function sendResponse($requestId, ResponseInterface $response)
      * @param int                    $requestId The request id to respond to
      * @param HttpFoundationResponse $response  The HTTP foundation response message
      */
-    private function sendHttpFoundationResponse($requestId, HttpFoundationResponse $response)
+    private function sendHttpFoundationResponse(int $requestId, HttpFoundationResponse $response): void
     {
         $statusCode = $response->getStatusCode();
 
diff --git a/src/Driver/Userland/ConnectionHandler/ConnectionHandlerFactory.php b/src/Driver/Userland/ConnectionHandler/ConnectionHandlerFactory.php
index c88e7bf..81dfca2 100644
--- a/src/Driver/Userland/ConnectionHandler/ConnectionHandlerFactory.php
+++ b/src/Driver/Userland/ConnectionHandler/ConnectionHandlerFactory.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\ConnectionHandler;
 
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\Connection\ConnectionInterface;
@@ -13,7 +15,7 @@ final class ConnectionHandlerFactory implements ConnectionHandlerFactoryInterfac
     /**
      * {@inheritdoc}
      */
-    public function createConnectionHandler(KernelInterface $kernel, ConnectionInterface $connection)
+    public function createConnectionHandler(KernelInterface $kernel, ConnectionInterface $connection): ConnectionHandlerInterface
     {
         return new ConnectionHandler($kernel, $connection);
     }
diff --git a/src/Driver/Userland/ConnectionHandler/ConnectionHandlerFactoryInterface.php b/src/Driver/Userland/ConnectionHandler/ConnectionHandlerFactoryInterface.php
index e7e0784..d46c6de 100644
--- a/src/Driver/Userland/ConnectionHandler/ConnectionHandlerFactoryInterface.php
+++ b/src/Driver/Userland/ConnectionHandler/ConnectionHandlerFactoryInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\ConnectionHandler;
 
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\Connection\ConnectionInterface;
@@ -19,5 +21,5 @@ interface ConnectionHandlerFactoryInterface
      *
      * @return ConnectionHandlerInterface The connection handler
      */
-    public function createConnectionHandler(KernelInterface $kernel, ConnectionInterface $connection);
+    public function createConnectionHandler(KernelInterface $kernel, ConnectionInterface $connection): ConnectionHandlerInterface;
 }
diff --git a/src/Driver/Userland/ConnectionHandler/ConnectionHandlerInterface.php b/src/Driver/Userland/ConnectionHandler/ConnectionHandlerInterface.php
index d4ed025..9b489fd 100644
--- a/src/Driver/Userland/ConnectionHandler/ConnectionHandlerInterface.php
+++ b/src/Driver/Userland/ConnectionHandler/ConnectionHandlerInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\ConnectionHandler;
 
 /**
@@ -16,18 +18,18 @@ interface ConnectionHandlerInterface
      *
      * @return int[] The status codes of requests dispatched during the function call
      */
-    public function ready();
+    public function ready(): array;
 
     /**
      * Gracefully shutdown the connection being handled.
      */
-    public function shutdown();
+    public function shutdown(): void;
 
     /**
      * Closes the connection handler and free's associated resources. Calling
      * this method must also close the connection object that was being handled.
      */
-    public function close();
+    public function close(): void;
 
     /**
      * Returns true if the connection handler has been closed and false if it
@@ -35,5 +37,5 @@ public function close();
      *
      * @return bool
      */
-    public function isClosed();
+    public function isClosed(): bool;
 }
diff --git a/src/Driver/Userland/Exception/ConnectionException.php b/src/Driver/Userland/Exception/ConnectionException.php
index b121c5e..a34a157 100644
--- a/src/Driver/Userland/Exception/ConnectionException.php
+++ b/src/Driver/Userland/Exception/ConnectionException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\Exception;
 
 /**
diff --git a/src/Driver/Userland/Exception/ProtocolException.php b/src/Driver/Userland/Exception/ProtocolException.php
index 303ea77..0924717 100644
--- a/src/Driver/Userland/Exception/ProtocolException.php
+++ b/src/Driver/Userland/Exception/ProtocolException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\Exception;
 
 /**
diff --git a/src/Driver/Userland/Exception/UserlandDaemonException.php b/src/Driver/Userland/Exception/UserlandDaemonException.php
index b8dc57a..46df451 100644
--- a/src/Driver/Userland/Exception/UserlandDaemonException.php
+++ b/src/Driver/Userland/Exception/UserlandDaemonException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland\Exception;
 
 use PHPFastCGI\FastCGIDaemon\Exception\DaemonException;
diff --git a/src/Driver/Userland/UserlandDaemon.php b/src/Driver/Userland/UserlandDaemon.php
index 9e52fcb..2a2a5c6 100644
--- a/src/Driver/Userland/UserlandDaemon.php
+++ b/src/Driver/Userland/UserlandDaemon.php
@@ -1,11 +1,14 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland;
 
 use PHPFastCGI\FastCGIDaemon\DaemonInterface;
 use PHPFastCGI\FastCGIDaemon\DaemonOptions;
 use PHPFastCGI\FastCGIDaemon\DaemonTrait;
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\Connection\ConnectionPoolInterface;
+use PHPFastCGI\FastCGIDaemon\Driver\Userland\ConnectionHandler\ConnectionHandler;
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\ConnectionHandler\ConnectionHandlerFactoryInterface;
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\Exception\UserlandDaemonException;
 use PHPFastCGI\FastCGIDaemon\Exception\ShutdownException;
@@ -65,7 +68,7 @@ public function __construct(KernelInterface $kernel, DaemonOptions $daemonOption
     /**
      * {@inheritdoc}
      */
-    public function run()
+    public function run(): void
     {
         $this->setupDaemon($this->daemonOptions);
         $this->daemonOptions->getOption(DaemonOptions::LOGGER)->notice('Daemon is running and ready to accept connections');
@@ -93,8 +96,10 @@ public function run()
      * Wait for connections in the pool to become readable. Create connection
      * handlers for new connections and trigger the ready method when there is
      * data for the handlers to receive. Clean up closed connections.
+     *
+     * @throws \Exception
      */
-    private function processConnectionPool()
+    private function processConnectionPool(): void
     {
         $readableConnections = $this->connectionPool->getReadableConnections(5);
 
@@ -118,8 +123,10 @@ private function processConnectionPool()
 
     /**
      * Gracefully shutdown the daemon.
+     *
+     * @throws \Exception
      */
-    private function shutdown()
+    private function shutdown(): void
     {
         $this->connectionPool->shutdown();
 
diff --git a/src/Driver/Userland/UserlandDaemonFactory.php b/src/Driver/Userland/UserlandDaemonFactory.php
index 964b482..7393424 100644
--- a/src/Driver/Userland/UserlandDaemonFactory.php
+++ b/src/Driver/Userland/UserlandDaemonFactory.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Driver\Userland;
 
 use PHPFastCGI\FastCGIDaemon\DaemonInterface;
@@ -26,7 +28,7 @@ final class UserlandDaemonFactory implements DaemonFactoryInterface
      *
      * @codeCoverageIgnore The FastCGI daemon
      */
-    public function createDaemon(KernelInterface $kernel, DaemonOptions $options, $fd = DaemonInterface::FCGI_LISTENSOCK_FILENO)
+    public function createDaemon(KernelInterface $kernel, DaemonOptions $options, int $fd = DaemonInterface::FCGI_LISTENSOCK_FILENO): DaemonInterface
     {
         $socket = fopen('php://fd/'.$fd, 'r');
 
@@ -51,7 +53,7 @@ public function createDaemon(KernelInterface $kernel, DaemonOptions $options, $f
      *
      * @codeCoverageIgnore
      */
-    public function createTcpDaemon(KernelInterface $kernel, DaemonOptions $options, $host, $port)
+    public function createTcpDaemon(KernelInterface $kernel, DaemonOptions $options, string $host, int $port): DaemonInterface
     {
         $address = 'tcp://'.$host.':'.$port;
         $socket  = stream_socket_server($address);
@@ -73,7 +75,7 @@ public function createTcpDaemon(KernelInterface $kernel, DaemonOptions $options,
      *
      * @return UserlandDaemon The FastCGI daemon
      */
-    public function createDaemonFromStreamSocket(KernelInterface $kernel, DaemonOptions $options, $socket)
+    public function createDaemonFromStreamSocket(KernelInterface $kernel, DaemonOptions $options, $socket): DaemonInterface
     {
         $connectionPool           = new StreamSocketConnectionPool($socket);
         $connectionHandlerFactory = new ConnectionHandlerFactory();
diff --git a/src/Exception/DaemonException.php b/src/Exception/DaemonException.php
index 000f759..375be46 100644
--- a/src/Exception/DaemonException.php
+++ b/src/Exception/DaemonException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Exception;
 
 /**
diff --git a/src/Exception/ShutdownException.php b/src/Exception/ShutdownException.php
index 0818050..919b2b8 100644
--- a/src/Exception/ShutdownException.php
+++ b/src/Exception/ShutdownException.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Exception;
 
 /**
diff --git a/src/Http/Request.php b/src/Http/Request.php
index 06354c4..bfeb10b 100644
--- a/src/Http/Request.php
+++ b/src/Http/Request.php
@@ -1,8 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Http;
 
 use Nyholm\Psr7Server\ServerRequestCreatorInterface;
+use Psr\Http\Message\ServerRequestInterface;
 use Symfony\Component\HttpFoundation\Request as HttpFoundationRequest;
 
 /**
@@ -67,7 +70,7 @@ public static function setServerRequestCreator(ServerRequestCreatorInterface $se
     /**
      * {@inheritdoc}
      */
-    public function getParams()
+    public function getParams(): array
     {
         return $this->params;
     }
@@ -108,7 +111,7 @@ public static function getUploadDir(): string
     /**
      * {@inheritdoc}
      */
-    public function getQuery()
+    public function getQuery(): array
     {
         $query = null;
 
@@ -122,7 +125,7 @@ public function getQuery()
     /**
      * {@inheritdoc}
      */
-    public function getPost()
+    public function getPost(): array
     {
         $post = null;
 
@@ -150,7 +153,7 @@ public function getPost()
         return $post ?: [];
     }
 
-    private function parseMultipartFormData($stream, $boundary) {
+    private function parseMultipartFormData($stream, string $boundary): array {
         $post = "";
         $files = [];
         $fieldType = $fieldName = $filename = $mimeType = null;
@@ -208,7 +211,7 @@ private function parseMultipartFormData($stream, $boundary) {
     /**
      * {@inheritdoc}
      */
-    public function getCookies()
+    public function getCookies(): array
     {
         $cookies = [];
 
@@ -235,7 +238,7 @@ public function getStdin()
     /**
      * {@inheritdoc}
      */
-    public function getServerRequest()
+    public function getServerRequest(): ServerRequestInterface
     {
         if (null === self::$serverRequestCreator) {
             throw new \RuntimeException('You need to add an object of \Nyholm\Psr7Server\ServerRequestCreatorInterface to \PHPFastCGI\FastCGIDaemon\Http\Request::setServerRequestCreator to use PSR-7 requests. Please install and read more at https://github.com/nyholm/psr7-server');
@@ -262,7 +265,7 @@ public function getServerRequest()
     /**
      * {@inheritdoc}
      */
-    public function getHttpFoundationRequest()
+    public function getHttpFoundationRequest(): HttpFoundationRequest
     {
         if (!class_exists(HttpFoundationRequest::class)) {
             throw new \RuntimeException('You need to install symfony/http-foundation:^4.0 to use HttpFoundation requests.');
diff --git a/src/Http/RequestInterface.php b/src/Http/RequestInterface.php
index e03c75f..4bfa020 100644
--- a/src/Http/RequestInterface.php
+++ b/src/Http/RequestInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon\Http;
 
 use Psr\Http\Message\ServerRequestInterface;
@@ -16,28 +18,22 @@ interface RequestInterface
      *
      * @return array Associative array of FastCGI request params
      */
-    public function getParams();
+    public function getParams(): array;
 
     /**
      * Returns expected contents of $_GET superglobal array.
-     *
-     * @return array
      */
-    public function getQuery();
+    public function getQuery(): array;
 
     /**
      * Returns expected contents of $_POST superglobal array.
-     *
-     * @return array
      */
-    public function getPost();
+    public function getPost(): array;
 
     /**
      * Returns expected contents of $_COOKIES superglobal.
-     *
-     * @return array
      */
-    public function getCookies();
+    public function getCookies(): array;
 
     /**
      * Get the FastCGI stdin data.
@@ -48,15 +44,11 @@ public function getStdin();
 
     /**
      * Get the request as a PSR-7 server request.
-     *
-     * @return ServerRequestInterface The request object
      */
-    public function getServerRequest();
+    public function getServerRequest(): ServerRequestInterface;
 
     /**
      * Get the request as a Symfony HttpFoundation request.
-     *
-     * @return HttpFoundationRequest The request object
      */
-    public function getHttpFoundationRequest();
+    public function getHttpFoundationRequest(): HttpFoundationRequest;
 }
diff --git a/src/KernelInterface.php b/src/KernelInterface.php
index d1129d8..ecfe806 100644
--- a/src/KernelInterface.php
+++ b/src/KernelInterface.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 namespace PHPFastCGI\FastCGIDaemon;
 
 use PHPFastCGI\FastCGIDaemon\Http\RequestInterface;
diff --git a/test/CallbackKernelTest.php b/test/CallbackKernelTest.php
index 6c55001..bea30e0 100644
--- a/test/CallbackKernelTest.php
+++ b/test/CallbackKernelTest.php
@@ -18,7 +18,7 @@ class CallbackKernelTest extends TestCase
      */
     public function testInvalidArgumentException()
     {
-        $this->expectException(\InvalidArgumentException::class);
+        $this->expectException(\TypeError::class);
         new CallbackKernel('not a callable function');
     }
 
diff --git a/test/Helper/Mocker/Driver/Connection/MockConnection.php b/test/Helper/Mocker/Driver/Connection/MockConnection.php
index 58b8baf..98d45f6 100644
--- a/test/Helper/Mocker/Driver/Connection/MockConnection.php
+++ b/test/Helper/Mocker/Driver/Connection/MockConnection.php
@@ -9,23 +9,23 @@ class MockConnection implements ConnectionInterface
 {
     use MockerTrait;
 
-    public function read($length)
+    public function read(int $length): string
     {
-        return $this->delegateCall('read', func_get_args());
+        $this->delegateCall('read', func_get_args());
     }
 
-    public function write($buffer)
+    public function write(string $buffer): void
     {
-        return $this->delegateCall('write', func_get_args());
+        $this->delegateCall('write', func_get_args());
     }
 
-    public function isClosed()
+    public function isClosed(): bool
     {
         return $this->delegateCall('isClosed', func_get_args());
     }
 
-    public function close()
+    public function close(): void
     {
-        return $this->delegateCall('close', func_get_args());
+        $this->delegateCall('close', func_get_args());
     }
 }
diff --git a/test/Helper/Mocker/Driver/Connection/MockConnectionPool.php b/test/Helper/Mocker/Driver/Connection/MockConnectionPool.php
index 12cb53e..a8a835d 100644
--- a/test/Helper/Mocker/Driver/Connection/MockConnectionPool.php
+++ b/test/Helper/Mocker/Driver/Connection/MockConnectionPool.php
@@ -9,23 +9,23 @@ class MockConnectionPool implements ConnectionPoolInterface
 {
     use MockerTrait;
 
-    public function getReadableConnections($timeout)
+    public function getReadableConnections(int $timeout): array
     {
         return $this->delegateCall('getReadableConnections', func_get_args());
     }
 
-    public function count()
+    public function count(): int
     {
         return $this->delegateCall('count', func_get_args());
     }
 
-    public function shutdown()
+    public function shutdown(): void
     {
-        return $this->delegateCall('shutdown', func_get_args());
+        $this->delegateCall('shutdown', func_get_args());
     }
 
-    public function close()
+    public function close(): void
     {
-        return $this->delegateCall('close', func_get_args());
+        $this->delegateCall('close', func_get_args());
     }
 }
diff --git a/test/Helper/Mocker/Driver/ConnectionHandler/MockConnectionHandler.php b/test/Helper/Mocker/Driver/ConnectionHandler/MockConnectionHandler.php
index d224d28..3c6e792 100644
--- a/test/Helper/Mocker/Driver/ConnectionHandler/MockConnectionHandler.php
+++ b/test/Helper/Mocker/Driver/ConnectionHandler/MockConnectionHandler.php
@@ -9,22 +9,22 @@ class MockConnectionHandler implements ConnectionHandlerInterface
 {
     use MockerTrait;
 
-    public function ready()
+    public function ready(): array
     {
         return $this->delegateCall('ready', func_get_args());
     }
 
-    public function shutdown()
+    public function shutdown(): void
     {
-        return $this->delegateCall('shutdown', func_get_args());
+        $this->delegateCall('shutdown', func_get_args());
     }
 
-    public function close()
+    public function close(): void
     {
-        return $this->delegateCall('close', func_get_args());
+        $this->delegateCall('close', func_get_args());
     }
 
-    public function isClosed()
+    public function isClosed(): bool
     {
         return $this->delegateCall('isClosed', func_get_args());
     }
diff --git a/test/Helper/Mocker/Driver/ConnectionHandler/MockConnectionHandlerFactory.php b/test/Helper/Mocker/Driver/ConnectionHandler/MockConnectionHandlerFactory.php
index 1bb4f84..51e094a 100644
--- a/test/Helper/Mocker/Driver/ConnectionHandler/MockConnectionHandlerFactory.php
+++ b/test/Helper/Mocker/Driver/ConnectionHandler/MockConnectionHandlerFactory.php
@@ -2,6 +2,7 @@
 
 namespace PHPFastCGI\Test\FastCGIDaemon\Helper\Mocker\Driver\ConnectionHandler;
 
+use PHPFastCGI\FastCGIDaemon\Driver\Userland\ConnectionHandler\ConnectionHandlerInterface;
 use PHPFastCGI\FastCGIDaemon\KernelInterface;
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\Connection\ConnectionInterface;
 use PHPFastCGI\FastCGIDaemon\Driver\Userland\ConnectionHandler\ConnectionHandlerFactoryInterface;
@@ -11,7 +12,7 @@ class MockConnectionHandlerFactory implements ConnectionHandlerFactoryInterface
 {
     use MockerTrait;
 
-    public function createConnectionHandler(KernelInterface $kernel, ConnectionInterface $connection)
+    public function createConnectionHandler(KernelInterface $kernel, ConnectionInterface $connection): ConnectionHandlerInterface
     {
         return $this->delegateCall('createConnectionHandler', func_get_args());
     }
diff --git a/test/Helper/Mocker/Driver/MockDriverContainer.php b/test/Helper/Mocker/Driver/MockDriverContainer.php
index 7536022..c431a24 100644
--- a/test/Helper/Mocker/Driver/MockDriverContainer.php
+++ b/test/Helper/Mocker/Driver/MockDriverContainer.php
@@ -2,6 +2,7 @@
 
 namespace PHPFastCGI\Test\FastCGIDaemon\Helper\Mocker\Driver;
 
+use PHPFastCGI\FastCGIDaemon\DaemonFactoryInterface;
 use PHPFastCGI\FastCGIDaemon\Driver\DriverContainerInterface;
 use PHPFastCGI\Test\FastCGIDaemon\Helper\Mocker\MockerTrait;
 
@@ -9,7 +10,7 @@ class MockDriverContainer implements DriverContainerInterface
 {
     use MockerTrait;
 
-    public function getFactory($driver)
+    public function getFactory(string $driver): DaemonFactoryInterface
     {
         return $this->delegateCall('getFactory', func_get_args());
     }
diff --git a/test/Helper/Mocker/MockDaemon.php b/test/Helper/Mocker/MockDaemon.php
index 8f3ca73..07c0a6c 100644
--- a/test/Helper/Mocker/MockDaemon.php
+++ b/test/Helper/Mocker/MockDaemon.php
@@ -8,13 +8,13 @@ class MockDaemon implements DaemonInterface
 {
     use MockerTrait;
 
-    public function run()
+    public function run(): void
     {
-        return $this->delegateCall('run', func_get_args());
+        $this->delegateCall('run', func_get_args());
     }
 
-    public function flagShutdown($message = null)
+    public function flagShutdown(string $message = null): void
     {
-        return $this->delegateCall('flagShutdown', func_get_args());
+        $this->delegateCall('flagShutdown', func_get_args());
     }
 }
diff --git a/test/Helper/Mocker/MockDaemonFactory.php b/test/Helper/Mocker/MockDaemonFactory.php
index 578164c..3343087 100644
--- a/test/Helper/Mocker/MockDaemonFactory.php
+++ b/test/Helper/Mocker/MockDaemonFactory.php
@@ -11,12 +11,12 @@ class MockDaemonFactory implements DaemonFactoryInterface
 {
     use MockerTrait;
 
-    public function createDaemon(KernelInterface $kernel, DaemonOptions $options, $fd = DaemonInterface::FCGI_LISTENSOCK_FILENO)
+    public function createDaemon(KernelInterface $kernel, DaemonOptions $options, int $fd = DaemonInterface::FCGI_LISTENSOCK_FILENO): DaemonInterface
     {
         return $this->delegateCall('createDaemon', func_get_args());
     }
 
-    public function createTcpDaemon(KernelInterface $kernel, DaemonOptions $options, $port, $host = 'localhost')
+    public function createTcpDaemon(KernelInterface $kernel, DaemonOptions $options, string $host = 'localhost', int $port): DaemonInterface
     {
         return $this->delegateCall('createTcpDaemon', func_get_args());
     }
diff --git a/test/Helper/Mocker/MockerTrait.php b/test/Helper/Mocker/MockerTrait.php
index 8f0957b..30a4d0b 100644
--- a/test/Helper/Mocker/MockerTrait.php
+++ b/test/Helper/Mocker/MockerTrait.php
@@ -41,7 +41,7 @@ public function __construct(array $callbacks = null)
      *
      * @throws \InvalidArgumentException When no callback is set for the method
      */
-    protected function delegateCall($method, $arguments)
+    protected function delegateCall(string $method, array $arguments)
     {
         if (!isset($this->callbacks[$method])) {
             throw new \InvalidArgumentException('Method not configured: '.$method);
@@ -61,7 +61,7 @@ protected function delegateCall($method, $arguments)
      *
      * @return array The delegated call list
      */
-    public function getDelegatedCalls()
+    public function getDelegatedCalls(): array
     {
         return $this->delegatedCalls;
     }