diff --git a/lib/compat/wordpress-5.9/block-template-utils.php b/lib/compat/wordpress-5.9/block-template-utils.php
index 2ecc53b121ade..37ae365ccc4f0 100644
--- a/lib/compat/wordpress-5.9/block-template-utils.php
+++ b/lib/compat/wordpress-5.9/block-template-utils.php
@@ -462,6 +462,7 @@ function _inject_theme_attribute_in_block_template_content( $template_content )
 	 */
 	function _remove_theme_attribute_in_block_template_content( $template_content ) {
 		$has_updated_content = false;
+		$new_content         = '';
 		$template_blocks     = parse_blocks( $template_content );
 
 		$blocks = _flatten_blocks( $template_blocks );
@@ -476,7 +477,11 @@ function _remove_theme_attribute_in_block_template_content( $template_content )
 			return $template_content;
 		}
 
-		return $template_content;
+		foreach ( $template_blocks as $block ) {
+			$new_content .= serialize_block( $block );
+		}
+
+		return $new_content;
 	}
 }