diff --git a/src/Ratchet/WebSocket/WsServer.php b/src/Ratchet/WebSocket/WsServer.php
index 144b914..4b2534c 100644
--- a/src/Ratchet/WebSocket/WsServer.php
+++ b/src/Ratchet/WebSocket/WsServer.php
@@ -208,7 +208,7 @@ class WsServer implements MessageComponentInterface {
             }
         }
 
-        return substr($string, 0, -1);
+        return substr($string, 0, -1) ?: '';
     }
 
     /**
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