diff --git a/packages/server/src/ChunkExtractor.js b/packages/server/src/ChunkExtractor.js
index 04110c21..6f54f8e8 100644
--- a/packages/server/src/ChunkExtractor.js
+++ b/packages/server/src/ChunkExtractor.js
@@ -11,6 +11,7 @@ import { smartRequire, joinURLPath } from './util'
 
 const EXTENSION_SCRIPT_TYPES = {
   '.js': 'script',
+  '.mjs': 'script',
   '.css': 'style',
 }