diff -u b/core/modules/config/lib/Drupal/config/Tests/ConfigLocaleOverrideWebTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigLocaleOverrideWebTest.php
--- b/core/modules/config/lib/Drupal/config/Tests/ConfigLocaleOverrideWebTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigLocaleOverrideWebTest.php
@@ -38,17 +38,21 @@
     // Add French and make it the site default language.
     $this->drupalPost('admin/config/regional/language/add', array('predefined_langcode' => 'fr'), t('Add language'));
 
-    // The log in block on the front page appears to use the system.site config
-    // object before language negotiation is finalized.
     $this->drupalLogout();
 
     // The home page in English should not have the override.
     $this->drupalGet('');
     $this->assertNoText('French site name');
 
-    // config_test module includes a locale.config.fr.system.site.yml which
-    // overrides the site name to 'French site name'. Ensure that it applies
-    // when we access the French page.
+    // During path resolution the system.site configuration object is used to
+    // determine the front page. This occurs before language negotiation causing
+    // the configuration factory to cache an object without the correct
+    // overrides. The config_test module includes a
+    // locale.config.fr.system.site.yml which overrides the site name to 'French
+    // site name' to test that the configuration factory is re-initialised
+    // language negotiation. Ensure that it applies when we access the French
+    // front page.
+    // @see \Drupal\Core\PathProcessor::processInbound()
     $this->drupalGet('fr');
     $this->assertText('French site name');
   }