diff --git a/wagtail/admin/static_src/wagtailadmin/js/page-editor.js b/wagtail/admin/static_src/wagtailadmin/js/page-editor.js
index dc42dc54b..d2913933f 100644
--- a/wagtail/admin/static_src/wagtailadmin/js/page-editor.js
+++ b/wagtail/admin/static_src/wagtailadmin/js/page-editor.js
@@ -241,15 +241,21 @@ function cleanForSlug(val, useURLify) {
     if (useURLify) {
         // URLify performs extra processing on the string (e.g. removing stopwords) and is more suitable
         // for creating a slug from the title, rather than sanitising a slug entered manually
-        return URLify(val, 255, unicodeSlugsEnabled);
-    } else {
-        // just do the "replace"
-        if (unicodeSlugsEnabled) {
-            return val.replace(/\s/g, '-').replace(/[&\/\\#,+()$~%.'":`@\^!*?<>{}]/g, '').toLowerCase();
-        } else {
-            return val.replace(/\s/g, '-').replace(/[^A-Za-z0-9\-\_]/g, '').toLowerCase();
+        let cleaned = URLify(val, 255, unicodeSlugsEnabled);
+
+        // if the result is blank (e.g. because the title consisted entirely of stopwords),
+        // fall through to the non-URLify method
+        if (cleaned) {
+            return cleaned;
         }
     }
+
+    // just do the "replace"
+    if (unicodeSlugsEnabled) {
+        return val.replace(/\s/g, '-').replace(/[&\/\\#,+()$~%.'":`@\^!*?<>{}]/g, '').toLowerCase();
+    } else {
+        return val.replace(/\s/g, '-').replace(/[^A-Za-z0-9\-\_]/g, '').toLowerCase();
+    }
 }
 
 function initSlugAutoPopulate() {