diff --git a/src/wp-includes/block-editor.php b/src/wp-includes/block-editor.php
index aaa249cb7b..50a20fcac7 100644
--- a/src/wp-includes/block-editor.php
+++ b/src/wp-includes/block-editor.php
@@ -468,6 +468,12 @@ function block_editor_rest_api_preload( array $preload_paths, $block_editor_cont
 	 */
 	$backup_global_post = ! empty( $post ) ? clone $post : $post;
 
+	foreach ( $preload_paths as &$path ) {
+		if ( ! str_starts_with( $path, '/' ) ) {
+			$path = '/' . $path;
+		}
+	}
+
 	$preload_data = array_reduce(
 		$preload_paths,
 		'rest_preload_api_request',