diff --git a/src/Messaging/MessageBuffer.php b/src/Messaging/MessageBuffer.php
index e6bf1ce..d761786 100644
--- a/src/Messaging/MessageBuffer.php
+++ b/src/Messaging/MessageBuffer.php
@@ -93,7 +93,7 @@ class MessageBuffer {
         $this->closeFrameChecker = $frameChecker;
         $this->checkForMask = (bool)$expectMask;
 
-        $this->exceptionFactory ?: $this->exceptionFactory = function($msg) {
+        $this->exceptionFactory ?: $exceptionFactory = function($msg) {
             return new \UnderflowException($msg);
         };