From 9540ea3b105b49c19ae3600b4f4edae1ec882e0c Mon Sep 17 00:00:00 2001
From: Will Lillis <will.lillis24@gmail.com>
Date: Sat, 29 Aug 2026 19:48:54 -0400
Subject: [PATCH] fix(lib): reject an `old_tree` from a different language

---
 lib/src/parser.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/src/parser.c b/lib/src/parser.c
index 08cb74392..e3540e1ef 100644
--- a/lib/src/parser.c
+++ b/lib/src/parser.c
@@ -2124,7 +2124,10 @@ TSTree *ts_parser_parse(
   TSInput input
 ) {
   TSTree *result = NULL;
-  if (!self->language || !input.read) return NULL;
+  if (
+    !self->language || !input.read ||
+    (old_tree && old_tree->language != self->language)
+  ) return NULL;
 
   if (ts_language_is_wasm(self->language)) {
     if (!self->wasm_store) return NULL;