diff --git a/src/types.d.ts b/src/types.d.ts
index c689870..afb8655 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -51,6 +51,7 @@ declare module "@codemirror/language" {
 	 */
 	interface ParseContext {
 		tree: Tree;
+		treeLen: number;
 	}
 }