diff --git a/lib/6to5/transformers/classes.js b/lib/6to5/transformers/classes.js
index 1ab7f74326..628f09ff03 100644
--- a/lib/6to5/transformers/classes.js
+++ b/lib/6to5/transformers/classes.js
@@ -31,9 +31,9 @@ var buildClass = function (node, file) {
   if (superName) {
     if (t.isMemberExpression(superName)) {
       superClassArgument = superClassCallee = getMemberExpressionObject(superName);
-    } else if (t.isIdentifier(superName)) {
+    } else if (!t.isIdentifier(superName)) {
       superClassArgument = superName;
-      superClassCallee = superName = b.identifier(file.generateUid("ref"));
+      superClassCallee   = superName = b.identifier(file.generateUid("ref"));
     }
   }