diff --git a/src/wp-includes/block-editor.php b/src/wp-includes/block-editor.php
index aaa249cb7b..13445af745 100644
--- a/src/wp-includes/block-editor.php
+++ b/src/wp-includes/block-editor.php
@@ -468,6 +468,22 @@ 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 ( is_string( $path ) && ! str_starts_with( $path, '/' ) ) {
+			$path = '/' . $path;
+		}
+
+		if ( is_array( $path ) ) {
+			foreach( $path as &$part ) {
+				if ( is_string( $part )
+					&& $path === strtolower( $part )
+					&& ! str_starts_with( $part ) ) {
+					$part = '/' . $part;
+				}
+			}
+		}
+	}
+
 	$preload_data = array_reduce(
 		$preload_paths,
 		'rest_preload_api_request',