diff --git a/packages/gatsby/src/internal-plugins/functions/index.ts b/packages/gatsby/src/internal-plugins/functions/index.js
similarity index 100%
rename from packages/gatsby/src/internal-plugins/functions/index.ts
rename to packages/gatsby/src/internal-plugins/functions/index.js
diff --git a/packages/gatsby/src/internal-plugins/functions/package.json b/packages/gatsby/src/internal-plugins/functions/package.json
index bd877f00cee68..5e97bd14dd8c9 100644
--- a/packages/gatsby/src/internal-plugins/functions/package.json
+++ b/packages/gatsby/src/internal-plugins/functions/package.json
@@ -2,7 +2,7 @@
   "name": "functions",
   "version": "1.0.0",
   "description": "An internal Gatsby plugin which lets one write serverless functions",
-  "main": "index.ts",
+  "main": "index.js",
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"
   },