diff --git a/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php b/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
index c3c83e1192..43f3611a1f 100644
--- a/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
+++ b/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
@@ -130,7 +130,12 @@ public function render(array $css_assets) {
           // assets: output a LINK tag for a file CSS asset.
           if (count($css_assets) <= 31) {
             $element = $link_element_defaults;
-            $element['#attributes']['href'] = file_url_transform_relative(file_create_url($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 (!isset($css_asset['preprocessed'])) {
+              $element['#attributes']['href'] .= $query_string_separator . $query_string;
+            }
             $element['#attributes']['media'] = $css_asset['media'];
             $element['#browsers'] = $css_asset['browsers'];
             $elements[] = $element;