diff --git a/core/modules/ckeditor/js/plugins/drupalimage/plugin.js b/core/modules/ckeditor/js/plugins/drupalimage/plugin.js
index 64ca8bb..047ae24 100644
--- a/core/modules/ckeditor/js/plugins/drupalimage/plugin.js
+++ b/core/modules/ckeditor/js/plugins/drupalimage/plugin.js
@@ -51,12 +51,7 @@
         var imgAttributes = widgetDefinition.allowedContent.img.attributes.split(/\s*,\s*/);
         for (var i = 0; i < imgAttributes.length; i++) {
           // Exclamation marks are only used in the string notation.
-          if (imgAttributes[i].substr(0, 1) === '!') {
-            allowedContentDefinition.attributes[imgAttributes[i].substr(1)] = '';
-          }
-          else {
-            allowedContentDefinition.attributes[imgAttributes[i]] = '';
-          }
+          allowedContentDefinition.attributes[imgAttributes[i].replace(/^!/, '')] = '';
         }
         if (widgetDefinition.allowedContent.img.classes) {
           allowedContentDefinition.attributes['class'] = widgetDefinition.allowedContent.img.classes.split(/\s*,\s*/).join(' ');