diff --git a/src/Plugin/UiPatterns/Source/BlockSource.php b/src/Plugin/UiPatterns/Source/BlockSource.php
index 7778585..fe7af29 100644
--- a/src/Plugin/UiPatterns/Source/BlockSource.php
+++ b/src/Plugin/UiPatterns/Source/BlockSource.php
@@ -150,6 +150,14 @@ class BlockSource extends SourcePluginBase implements SourceWithChoicesInterface
       return [];
     }
     $build = $this->block->build();
+
+    // Allow other modules to alter the block build.
+    $this->moduleHandler->alter(
+      ['block_view', 'block_view_' . $this->block->getBaseId()],
+      $build,
+      $this->block
+    );
+
     if (!is_array($build)) {
       return [];
     }