diff -u b/core/modules/filter/filter.module b/core/modules/filter/filter.module
--- b/core/modules/filter/filter.module
+++ b/core/modules/filter/filter.module
@@ -836,8 +836,8 @@
   $image->setAttribute('title', t('This image has been removed. For security reasons, only images from the local domain are allowed.'));
   $image_factory = \Drupal::service('image.factory');
   $error_image = $image_factory->get('core/misc/icons/ea2800/error.svg');
-  $image->setAttribute('height', '16px');
-  $image->setAttribute('width',  '16px');
+  $image->setAttribute('height', '16');
+  $image->setAttribute('width',  '16');
 
   // Add a CSS class to aid in styling.
   $class = ($image->getAttribute('class') ? trim($image->getAttribute('class')) . ' ' : '');