diff --git a/lib/common/options.mjs b/lib/common/options.mjs
index ed5b0c8135..624f427ad0 100644
--- a/lib/common/options.mjs
+++ b/lib/common/options.mjs
@@ -77,6 +77,10 @@ Options.from = function (_options) {
     options.extensions.unshift('js')
   }
 
+  if (options.extensions.indexOf('mjs') === -1) {
+    options.extensions.unshift('mjs')
+  }
+
   // If app.html is defined, set the template path to the user template
   options.appTemplatePath = path.resolve(options.buildDir, 'views/app.template.html')
   if (fs.existsSync(path.join(options.srcDir, 'app.html'))) {