diff --git a/src/Service/BlockClassHelperService.php b/src/Service/BlockClassHelperService.php
index bac9bb0..58ada55 100644
--- a/src/Service/BlockClassHelperService.php
+++ b/src/Service/BlockClassHelperService.php
@@ -199,7 +199,15 @@ class BlockClassHelperService {
       $current_block_classes = explode(' ', $block_classes ?? '');
 
       // Merge with the current one.
-      $block_classes_to_store = array_merge($block_classes_stored, $current_block_classes);
+      // If is an array proceed.
+      if (is_array($block_classes_stored)) {
+        $block_classes_to_store = array_merge($block_classes_stored, $current_block_classes);
+      }
+
+      if (!is_array($block_classes_stored)) {
+        array_push($current_block_classes, $block_classes_stored);
+        $block_classes_to_store = $current_block_classes;
+      }
       $block_classes_to_store = array_unique($block_classes_to_store);
 
       // Store in the config.