diff --git a/lib/typescript-preprocessor.js b/lib/typescript-preprocessor.js
index d3aa069e3..d92c53b67 100644
--- a/lib/typescript-preprocessor.js
+++ b/lib/typescript-preprocessor.js
@@ -15,6 +15,7 @@ class TypeScriptPreprocessor {
   constructor(options) {
     this.name = 'ember-cli-typescript';
     this._tag = tag++;
+    this.ext = 'ts';
 
     // Update the config for how Broccoli handles the file system: no need for
     // includes, always emit, and let Broccoli manage any outDir.