diff --git a/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php b/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
index d042176d09..5e5c5cbc88 100644
--- a/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
+++ b/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
@@ -55,10 +55,13 @@ public function render(array $css_assets) {
       switch ($css_asset['type']) {
         // For file items, output a LINK tag for file CSS assets.
         case 'file':
-          // The dummy query string needs to be added to the URL to control
-          // browser-caching.
-          $query_string_separator = (strpos($css_asset['data'], '?') !== FALSE) ? '&' : '?';
-          $element['#attributes']['href'] = file_url_transform_relative(file_create_url($css_asset['data'])) . $query_string_separator . $query_string;
+          $element['#attributes']['href'] = file_url_transform_relative(file_create_url($css_asset['data']));
+          // Only add the cache-busting query string if this isn't an aggregate
+          // file.
+          if (!$css_asset['preprocessed']) {
+            $query_string_separator = (strpos($css_asset['data'], '?') !== FALSE) ? '&' : '?';
+            $element['#attributes']['href'] .= $query_string_separator . $query_string;
+          }
           break;
 
         case 'external':