diff --git a/src/babel/build-external-helpers.js b/src/babel/build-external-helpers.js
index 89fbb08bbd..b96579a27f 100644
--- a/src/babel/build-external-helpers.js
+++ b/src/babel/build-external-helpers.js
@@ -1,5 +1,6 @@
 import buildHelpers from "./build-helpers";
 import generator from "./generation";
+import * as messages from "./messages";
 import * as util from  "./util";
 import t from "./types";
 
@@ -62,7 +63,7 @@ export default function (whitelist, outputType = "global") {
   } else if (outputType === "var") {
     tree = buildVar(namespace, builder);
   } else {
-    throw new Error("Unsupported output type");
+    throw new Error(messages.get("unsupportedOutputType", outputType));
   }
 
   return generator(tree).code;
diff --git a/src/babel/messages.js b/src/babel/messages.js
index cf00085320..0f70f1410f 100644
--- a/src/babel/messages.js
+++ b/src/babel/messages.js
@@ -20,7 +20,8 @@ export var messages = {
   didYouMean: "Did you mean $1?",
   evalInStrictMode: "eval is not allowed in strict mode",
   codeGeneratorDeopt: "Note: The code generator has deoptimised the styling of $1 as it exceeds the max of $2.",
-  missingTemplatesDirectory: "no templates directory - this is most likely the result of a broken `npm publish`. Please report to https://github.com/babel/babel/issues"
+  missingTemplatesDirectory: "no templates directory - this is most likely the result of a broken `npm publish`. Please report to https://github.com/babel/babel/issues",
+  unsupportedOutputType: "Unsupported output type $1"
 };
 
 export function get(key) {