diff --git a/src/Ratchet/WebSocket/WsServer.php b/src/Ratchet/WebSocket/WsServer.php
index fa36e5f..61d42b6 100644
--- a/src/Ratchet/WebSocket/WsServer.php
+++ b/src/Ratchet/WebSocket/WsServer.php
@@ -65,6 +65,7 @@ class WsServer implements HttpServerInterface {
 
         $this->closeFrameChecker   = new CloseFrameChecker;
         $this->handshakeNegotiator = new ServerNegotiator(new RequestVerifier);
+        $this->handshakeNegotiator->setStrictSubProtocolCheck(true);
 
         if ($component instanceof WsServerInterface) {
             $this->handshakeNegotiator->setSupportedSubProtocols($component->getSubProtocols());
@@ -202,4 +203,4 @@ class WsServer implements HttpServerInterface {
             }
         });
    }
-}
\ No newline at end of file
+}