diff --git a/core/modules/simpletest/src/TestBase.php b/core/modules/simpletest/src/TestBase.php
index e822adb..1354d5a 100644
--- a/core/modules/simpletest/src/TestBase.php
+++ b/core/modules/simpletest/src/TestBase.php
@@ -209,7 +209,7 @@
    *
    * @var bool
    */
-  protected $strictConfigSchema = FALSE;
+  protected $strictConfigSchema = TRUE;
 
   /**
    * Constructor for Test.