diff --git a/Gruntfile.coffee b/Gruntfile.coffee
index 76b6983c0..2b690a697 100644
--- a/Gruntfile.coffee
+++ b/Gruntfile.coffee
@@ -46,7 +46,7 @@ module.exports = (grunt)->
             dev:
                 options:
                     sourceMap: true
-                files: [expand:true, cwd:'./src/coffee', src:'**/*.coffee', dest:'./dist']
+                files: [expand:true, cwd:'./src/coffee', src:'**/*.coffee', dest:'./dist', ext:'.js']
 
         clean:
             dist: ['./dist']