core/modules/block/tests/modules/block_test/block_test.module | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/core/modules/block/tests/modules/block_test/block_test.module b/core/modules/block/tests/modules/block_test/block_test.module
index 7f058b6..284b836 100644
--- a/core/modules/block/tests/modules/block_test/block_test.module
+++ b/core/modules/block/tests/modules/block_test/block_test.module
@@ -41,7 +41,7 @@ function block_test_block_build_test_cache_alter(array &$build, BlockPluginInter
     $build['#cache']['contexts'][] = \Drupal::state()->get('block_test_block_alter_cache_context');
   }
   if (\Drupal::state()->get('block_test_block_alter_cache_tag') !== NULL) {
-    $build['#cache']['tags'][] = \Drupal::state()->get('block_test_block_alter_cache_tag');
+    $build['#cache']['tags'] = Cache::mergeTags($build['#cache']['tags'], [\Drupal::state()->get('block_test_block_alter_cache_tag')]);
   }
   if (\Drupal::state()->get('block_test_block_alter_cache_max_age') !== NULL) {
     $build['#cache']['max-age'] = \Drupal::state()->get('block_test_block_alter_cache_max_age');