diff --git a/altair/expr/core.py b/altair/expr/core.py
index e3bc65a52..e7872ada6 100644
--- a/altair/expr/core.py
+++ b/altair/expr/core.py
@@ -237,4 +237,4 @@ def __repr__(self) -> str:
         return f"{self.group}[{self.name!r}]"
 
 
-IntoExpression: TypeAlias = Union[bool, None, str, OperatorMixin, Dict[str, Any]]
+IntoExpression: TypeAlias = Union[bool, None, str, float, OperatorMixin, Dict[str, Any]]