diff --git a/lib/6to5/transformation/file.js b/lib/6to5/transformation/file.js
index 03265bea7b..57cdf6ea49 100644
--- a/lib/6to5/transformation/file.js
+++ b/lib/6to5/transformation/file.js
@@ -297,7 +297,7 @@ File.prototype.isConsequenceExpressionStatement = function (node) {
 
 File.prototype.addHelper = function (name) {
   if (!contains(File.helpers, name)) {
-    throw new ReferenceError("unknown declaration " + name);
+    throw new ReferenceError("unknown helper " + name);
   }
 
   var program = this.ast.program;