diff --git a/app/assets/javascripts/discourse/components/composer-editor.js.es6 b/app/assets/javascripts/discourse/components/composer-editor.js.es6
index be2b1df3d5d..4b95913aa45 100644
--- a/app/assets/javascripts/discourse/components/composer-editor.js.es6
+++ b/app/assets/javascripts/discourse/components/composer-editor.js.es6
@@ -214,7 +214,8 @@ export default Ember.Component.extend({
     const previewOffsetTop = $preview.offset().top;
     const offset = $preview.scrollTop() - previewOffsetTop - ($input.offset().top - previewOffsetTop);
     const nonEmptyList = [];
-    const scrollMap = Array(numberOfLines).fill(-1);
+    const scrollMap = [];
+    for (let i = 0; i < numberOfLines; i++) { scrollMap.push(-1); };
 
     nonEmptyList.push(0);
     scrollMap[0] = 0;