diff --git a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
index b26e894536..bda234e3f8 100644
--- a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
+++ b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
@@ -494,12 +494,12 @@ protected function setOverrideValue(array $overrides, $type, $library_name, $ext
       // library definition path.
 
       // For BC we check if $original still refers to base-theme overrides.
-      // @todo Remove BC in Drupal 9.0.0 https://www.drupal.org/node/2852314.
+      // @todo Remove BC in Drupal 10.0.0 https://www.drupal.org/node/2852314.
       if (isset($this->originalLibraryPaths[$original])) {
         // Here $original actually refers to an overridden path (maybe from a
         // base theme), so get the actual original path by which the library
         // asset was keyed.
-        @trigger_error('Overriding a library asset using an overridden path as key is deprecated, please use the original path as key.', E_USER_DEPRECATED);
+        @trigger_error(sprintf('Overriding a library asset using an overridden path as the key is deprecated, please use the original path (%s) as the key.', $original), E_USER_DEPRECATED);
         $original = $this->originalLibraryPaths[$original];
       }
       if ($replacement) {
diff --git a/core/modules/system/tests/themes/test_theme/test_theme.info.yml b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
index c375cafa6f..a7067350c5 100644
--- a/core/modules/system/tests/themes/test_theme/test_theme.info.yml
+++ b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
@@ -37,7 +37,7 @@ libraries-override:
   system/base:
     css:
       component:
-        /core/themes/stable/css/system/components/js.module.css: false
+        css/system/components/js.module.css: false
   # It works for JS as well.
   core/jquery:
     js: