diff --git a/msgspec/__init__.pyi b/msgspec/__init__.pyi
index 4d2d8744..8f8b6cc3 100644
--- a/msgspec/__init__.pyi
+++ b/msgspec/__init__.pyi
@@ -25,6 +25,8 @@ T = TypeVar("T")
 class UnsetType(enum.Enum):
     UNSET = "UNSET"
 
+    def __bool__() -> Literal[False]:...
+
 UNSET = UnsetType.UNSET
 
 class _NoDefault(enum.Enum):