diff --git a/src/Plugin/ContextReaction/Blocks.php b/src/Plugin/ContextReaction/Blocks.php
index 071dffe..ee18ffd 100644
--- a/src/Plugin/ContextReaction/Blocks.php
+++ b/src/Plugin/ContextReaction/Blocks.php
@@ -218,6 +218,9 @@ class Blocks extends ContextReactionPluginBase implements ContainerFactoryPlugin
           ],
         ];
 
+        // Allow altering of cacheability metadata or setting #create_placeholder.
+        \Drupal::moduleHandler()->alter(['block_build', "block_build_" . $block->getBaseId()], $blockBuild, $block);
+
         // Add contextual links to block.
         $content = $block->build();
         if (isset($content['#contextual_links'])) {