diff --git a/protocol_test.go b/protocol_test.go
new file mode 100644
index 0000000..22dd56b
--- /dev/null
+++ b/protocol_test.go
@@ -0,0 +1,57 @@
+package cmux
+
+import (
+	"net"
+	"testing"
+)
+
+func TestMuxConn_CheckPrefix(t *testing.T) {
+	// Create a listener on a random port
+	listener, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("failed to create listener: %v", err)
+	}
+
+	go func() {
+		// Accept a connection from the listener
+		conn, err := listener.Accept()
+		if err != nil {
+			t.Errorf("failed to accept connection: %v", err)
+			return
+		}
+
+		// Write a PROXY header to the connection
+		_, err = conn.Write([]byte("PROXY TCP4 192.168.1.1 192.168.1.2 1234 5678\r\n"))
+		if err != nil {
+			t.Errorf("failed to write PROXY header: %v", err)
+			return
+		}
+
+		// Close the connection
+		conn.Close()
+	}()
+
+	// Dial the listener with a MuxConn
+	conn, err := net.Dial("tcp", listener.Addr().String())
+	if err != nil {
+		t.Fatalf("failed to dial listener: %v", err)
+	}
+
+	muxConn := newMuxConn(conn)
+
+	// Call checkPrefix to parse the PROXY header
+	err = muxConn.checkPrefix()
+	if err != nil {
+		t.Errorf("checkPrefix returned error: %v", err)
+	}
+
+	// Verify the source and destination addresses were parsed correctly
+	expectedSrc := "192.168.1.1:1234"
+	expectedDst := "192.168.1.2:5678"
+	if muxConn.RemoteAddr().String() != expectedSrc {
+		t.Errorf("RemoteAddr() returned %s, expected %s", muxConn.RemoteAddr().String(), expectedSrc)
+	}
+	if muxConn.LocalAddr().String() != expectedDst {
+		t.Errorf("LocalAddr() returned %s, expected %s", muxConn.LocalAddr().String(), expectedDst)
+	}
+}