diff --git a/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
index 3f686e7..0957169 100644
--- a/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -521,8 +521,7 @@ protected function enableModules(array $modules) {
       $extensions['versions'][$module] = [
         'current' => $version,
         'install' => $version,
-        // @todo How to get schema - or should installSchema do this?
-        'schema' => SCHEMA_UNINSTALLED,
+        'schema' => (string) SCHEMA_UNINSTALLED,
       ];
     }
     $active_storage->write('core.extension', $extensions);
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index 0149613..bb3db18 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -834,8 +834,7 @@ protected function enableModules(array $modules) {
       $extension_config['versions'][$module] = [
         'current' => $version,
         'install' => $version,
-        // @todo How to get schema - or should installSchema do this?
-        'schema' => SCHEMA_UNINSTALLED,
+        'schema' => (string) SCHEMA_UNINSTALLED,
       ];
     }
     $active_storage->write('core.extension', $extension_config);