diff --git a/sinon-spy-react.js b/sinon-spy-react.js
index <HASH>..<HASH> 100644
--- a/sinon-spy-react.js
+++ b/sinon-spy-react.js
@@ -17,7 +17,7 @@ function spyOnReactClass(reactClass, methodName) {
 
 function reactClassPrototype(reactClass) {
     var ctor = reactClass.prototype && reactClass.prototype.constructor;
-    if (typeof ctor === 'undefinied')
+    if (typeof ctor === 'undefined')
         throw new Error('A component constructor could not be found for this class. Are you sure you passed in a React component?');
 
     return ctor.prototype;
Corrected check for constructor existence