diff --git a/src/workerd/api/global-scope.h b/src/workerd/api/global-scope.h
index 4498839b4c8..545fc370901 100644
--- a/src/workerd/api/global-scope.h
+++ b/src/workerd/api/global-scope.h
@@ -565,7 +565,7 @@ struct ExportedHandler {
     type ExportedHandlerConnectHandler<Env = unknown, Props = unknown> = (socket: Socket, env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
     type ExportedHandlerTailHandler<Env = unknown, Props = unknown> = (events: TraceItem[], env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
     type ExportedHandlerTraceHandler<Env = unknown, Props = unknown> = (traces: TraceItem[], env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
-    type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (event : TailStream.TailEvent<TailStream.Onset>, env: Env, ctx: ExecutionContext<Props>) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
+    type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (event : TailStream.TailEvent<TailStream.Onset>, env: Env, ctx: ExecutionContext<Props>) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType> | undefined;
     type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (controller: ScheduledController, env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
     type ExportedHandlerQueueHandler<Env = unknown, Message = unknown, Props = unknown> = (batch: MessageBatch<Message>, env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
     type ExportedHandlerTestHandler<Env = unknown, Props = unknown> = (controller: TestController, env: Env, ctx: ExecutionContext<Props>) => void | Promise<void>;
diff --git a/types/defines/rpc.d.ts b/types/defines/rpc.d.ts
index fd1409e0aa6..44477bfdccf 100644
--- a/types/defines/rpc.d.ts
+++ b/types/defines/rpc.d.ts
@@ -243,7 +243,7 @@ declare namespace CloudflareWorkersModule {
     queue?(batch: MessageBatch): void | Promise<void>;
     scheduled?(controller: ScheduledController): void | Promise<void>;
     tail?(events: TraceItem[]): void | Promise<void>;
-    tailStream?(event: TailStream.TailEvent<TailStream.Onset>): TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
+    tailStream?(event: TailStream.TailEvent<TailStream.Onset>): TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType> | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }
diff --git a/types/generated-snapshot/experimental/index.d.ts b/types/generated-snapshot/experimental/index.d.ts
index 2d13a470932..2efbf08344c 100755
--- a/types/generated-snapshot/experimental/index.d.ts
+++ b/types/generated-snapshot/experimental/index.d.ts
@@ -532,7 +532,10 @@ type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (
   event: TailStream.TailEvent<TailStream.Onset>,
   env: Env,
   ctx: ExecutionContext<Props>,
-) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
+) =>
+  | TailStream.TailEventHandlerType
+  | Promise<TailStream.TailEventHandlerType>
+  | undefined;
 type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (
   controller: ScheduledController,
   env: Env,
@@ -16196,7 +16199,8 @@ declare namespace CloudflareWorkersModule {
       event: TailStream.TailEvent<TailStream.Onset>,
     ):
       | TailStream.TailEventHandlerType
-      | Promise<TailStream.TailEventHandlerType>;
+      | Promise<TailStream.TailEventHandlerType>
+      | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }
diff --git a/types/generated-snapshot/experimental/index.ts b/types/generated-snapshot/experimental/index.ts
index 402342e9c94..2ac4820f822 100755
--- a/types/generated-snapshot/experimental/index.ts
+++ b/types/generated-snapshot/experimental/index.ts
@@ -534,7 +534,10 @@ export type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (
   event: TailStream.TailEvent<TailStream.Onset>,
   env: Env,
   ctx: ExecutionContext<Props>,
-) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
+) =>
+  | TailStream.TailEventHandlerType
+  | Promise<TailStream.TailEventHandlerType>
+  | undefined;
 export type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (
   controller: ScheduledController,
   env: Env,
@@ -16137,7 +16140,8 @@ export declare namespace CloudflareWorkersModule {
       event: TailStream.TailEvent<TailStream.Onset>,
     ):
       | TailStream.TailEventHandlerType
-      | Promise<TailStream.TailEventHandlerType>;
+      | Promise<TailStream.TailEventHandlerType>
+      | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }
diff --git a/types/generated-snapshot/index.d.ts b/types/generated-snapshot/index.d.ts
index ec0b5782110..a520e050d45 100755
--- a/types/generated-snapshot/index.d.ts
+++ b/types/generated-snapshot/index.d.ts
@@ -531,7 +531,10 @@ type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (
   event: TailStream.TailEvent<TailStream.Onset>,
   env: Env,
   ctx: ExecutionContext<Props>,
-) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
+) =>
+  | TailStream.TailEventHandlerType
+  | Promise<TailStream.TailEventHandlerType>
+  | undefined;
 type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (
   controller: ScheduledController,
   env: Env,
@@ -15913,7 +15916,8 @@ declare namespace CloudflareWorkersModule {
       event: TailStream.TailEvent<TailStream.Onset>,
     ):
       | TailStream.TailEventHandlerType
-      | Promise<TailStream.TailEventHandlerType>;
+      | Promise<TailStream.TailEventHandlerType>
+      | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }
diff --git a/types/generated-snapshot/index.ts b/types/generated-snapshot/index.ts
index 4b0698eef97..6d29dc9c0b2 100755
--- a/types/generated-snapshot/index.ts
+++ b/types/generated-snapshot/index.ts
@@ -533,7 +533,10 @@ export type ExportedHandlerTailStreamHandler<Env = unknown, Props = unknown> = (
   event: TailStream.TailEvent<TailStream.Onset>,
   env: Env,
   ctx: ExecutionContext<Props>,
-) => TailStream.TailEventHandlerType | Promise<TailStream.TailEventHandlerType>;
+) =>
+  | TailStream.TailEventHandlerType
+  | Promise<TailStream.TailEventHandlerType>
+  | undefined;
 export type ExportedHandlerScheduledHandler<Env = unknown, Props = unknown> = (
   controller: ScheduledController,
   env: Env,
@@ -15854,7 +15857,8 @@ export declare namespace CloudflareWorkersModule {
       event: TailStream.TailEvent<TailStream.Onset>,
     ):
       | TailStream.TailEventHandlerType
-      | Promise<TailStream.TailEventHandlerType>;
+      | Promise<TailStream.TailEventHandlerType>
+      | undefined;
     test?(controller: TestController): void | Promise<void>;
     trace?(traces: TraceItem[]): void | Promise<void>;
   }