diff --git a/lib/core/scxml/SCXML.js b/lib/core/scxml/SCXML.js
index 8562488f..bc5b0979 100644
--- a/lib/core/scxml/SCXML.js
+++ b/lib/core/scxml/SCXML.js
@@ -560,7 +560,13 @@ SCXMLInterpreter.prototype = {
 
     /** @expose */
     unregisterListener : function(listener){
-        return this._listeners.splice(this._listeners.indexOf(listener),1);
+        var retval;
+        var index = this._listeners.indexOf(listener);
+        if (index >= 0) {
+          retval = this._listeners.splice(index,1);
+        }
+
+        return retval;
     }
 
 };