diff --git a/wagtail/admin/static_src/wagtailadmin/js/page-editor.js b/wagtail/admin/static_src/wagtailadmin/js/page-editor.js
index 64c1b7bb0..824ce6f4f 100644
--- a/wagtail/admin/static_src/wagtailadmin/js/page-editor.js
+++ b/wagtail/admin/static_src/wagtailadmin/js/page-editor.js
@@ -412,4 +412,6 @@ $(function() {
     });
 });
 
-module.exports.cleanForSlug = cleanForSlug;
+if (typeof module !== 'undefined' && module.exports) {
+  module.exports.cleanForSlug = cleanForSlug;
+}