diff --git a/src/Ratchet/WebSocket/WsServer.php b/src/Ratchet/WebSocket/WsServer.php
index 144b914..7577ef6 100644
--- a/src/Ratchet/WebSocket/WsServer.php
+++ b/src/Ratchet/WebSocket/WsServer.php
@@ -200,15 +200,15 @@ class WsServer implements MessageComponentInterface {
             return '';
         }
 
-        $string = '';
+        $result = array();
 
         foreach ($requested as $sub) {
             if ($this->isSubProtocolSupported($sub)) {
-                $string .= $sub . ',';
+                $result[] = $sub;
             }
         }
 
-        return substr($string, 0, -1);
+        return implode(',', $result);
     }
 
     /**
diff --git a/tests/Ratchet/Tests/WebSocket/WsServerTest.php b/tests/Ratchet/Tests/WebSocket/WsServerTest.php
index b02e301..510b5aa 100644
--- a/tests/Ratchet/Tests/WebSocket/WsServerTest.php
+++ b/tests/Ratchet/Tests/WebSocket/WsServerTest.php
@@ -45,6 +45,6 @@ class WsServerTest extends \PHPUnit_Framework_TestCase {
         $method = $class->getMethod('getSubProtocolString');
         $method->setAccessible(true);
 
-        $this->assertEquals($expected, $method->invokeArgs($this->serv, array($req)));
+        $this->assertSame($expected, $method->invokeArgs($this->serv, array($req)));
     }
 }
\ No newline at end of file