diff --git a/core/modules/system/system.install b/core/modules/system/system.install
index 07efd6d..c5a6228 100644
--- a/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -1985,6 +1985,8 @@ function system_update_8014() {
     '1' => 'some',
     '2' => 'all',
     '3' => 'verbose',
+    // Also map the system.logging:error_level default value.
+    'all' => 'all',
   );
   $config->set('error_level', $map[$config->get('error_level')]);
   $config->save();