diff --git a/pyproject.toml b/pyproject.toml
index efa1d76..b27f453 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -27,6 +27,7 @@ dependencies = [
     "packaging",
     "tokenizers",
     "formatron",
+    "kbnf>=0.4.1",
     "aiofiles",
     "aiohttp",
     "async_lru",