diff --git a/internal/cli/run_test.go b/internal/cli/run_test.go
index aa0d4b0..76c14fc 100644
--- a/internal/cli/run_test.go
+++ b/internal/cli/run_test.go
@@ -1,10 +1,13 @@
 package cli
 
 import (
+	"io"
 	"io/ioutil"
+	"net"
 	"net/http"
 	"os"
 	"sync"
+	"syscall"
 	"testing"
 	"time"
 
@@ -238,3 +241,13 @@ func TestNormalize(t *testing.T) {
 		}
 	}
 }
+
+func TestProtocolNotSupported(t *testing.T) {
+	if protocolNotSupported(io.EOF) {
+		t.Error("EOF considered as protocol not supported")
+	}
+	err := &net.OpError{Op: "listen", Err: syscall.EPROTONOSUPPORT}
+	if !protocolNotSupported(err) {
+		t.Errorf("result for %v should be true", err)
+	}
+}