diff --git a/src/Ratchet/WebSocket/Version/HyBi10.php b/src/Ratchet/WebSocket/Version/HyBi10.php
index f557a18..0ac41fa 100644
--- a/src/Ratchet/WebSocket/Version/HyBi10.php
+++ b/src/Ratchet/WebSocket/Version/HyBi10.php
@@ -4,11 +4,11 @@ use Guzzle\Http\Message\RequestInterface;
 
 class HyBi10 extends RFC6455 {
     public function isProtocol(RequestInterface $request) {
-        $version = (int)$request->getHeader('Sec-WebSocket-Version', -1);
+        $version = (int)((string)($request->getHeader('Sec-WebSocket-Version', -1)));
         return ($version >= 6 && $version < 13);
     }
 
     public function getVersionNumber() {
         return 6;
     }
-}
\ No newline at end of file
+}