diff --git a/src/wp-includes/class-wp-block-supports.php b/src/wp-includes/class-wp-block-supports.php
index afc011803b0ff..c90b5e0c54c59 100644
--- a/src/wp-includes/class-wp-block-supports.php
+++ b/src/wp-includes/class-wp-block-supports.php
@@ -103,7 +103,7 @@ public function apply_block_supports() {
 			return array();
 		}
 
-		$block_attributes = array_key_exists( 'attrs', self::$block_to_render )
+		$block_attributes = array_key_exists( 'attrs', self::$block_to_render ) && is_array( self::$block_to_render['attrs'] )
 			? self::$block_to_render['attrs']
 			: array();