diff --git a/lodash.js b/lodash.js
index e64f40137..0420c8149 100644
--- a/lodash.js
+++ b/lodash.js
@@ -6013,7 +6013,7 @@
       getTag = function(value) {
         var result = baseGetTag(value),
             Ctor = result == objectTag ? value.constructor : undefined,
-            ctorString = Ctor ? toSource(Ctor) : undefined;
+            ctorString = Ctor ? toSource(Ctor) : '';
 
         if (ctorString) {
           switch (ctorString) {