diff --git a/core/lib/Drupal/Core/Config/TypedConfigManager.php b/core/lib/Drupal/Core/Config/TypedConfigManager.php
index 0a8f8f4..98e8417 100644
--- a/core/lib/Drupal/Core/Config/TypedConfigManager.php
+++ b/core/lib/Drupal/Core/Config/TypedConfigManager.php
@@ -302,7 +302,7 @@ public function hasConfigSchema($name) {
   protected function alterDefintions(&$definitions) {
     $discovered_schema = array_keys($definitions);
     parent::alterDefintions($definitions);
-    if ($discovered_schema !== array_keys($definitions)) {
+    if ($discovered_schema != array_keys($definitions)) {
       throw new ConfigSchemaAlterException('Invoking hook_config_schema_info_alter() has added or removed schema definitions');
     }
   }
diff --git a/core/modules/config/tests/config_schema_test/config_schema_test.module b/core/modules/config/tests/config_schema_test/config_schema_test.module
index e697f9c..3962cf4 100644
--- a/core/modules/config/tests/config_schema_test/config_schema_test.module
+++ b/core/modules/config/tests/config_schema_test/config_schema_test.module
@@ -12,7 +12,9 @@ function config_schema_test_config_schema_info_alter(&$definitions) {
   if (\Drupal::state()->get('config_schema_test_exception')) {
     unset($definitions['config_schema_test.hook']);
   }
-  else {
+
+  // Since code can not be unloaded only alter the definition if it exists.
+  if (isset($definitions['config_schema_test.hook'])) {
     $definitions['config_schema_test.hook']['additional_metadata'] = 'new schema info';
   }
 }