diff --git a/clvm/SExp.py b/clvm/SExp.py
index 398fe108..44022ba1 100644
--- a/clvm/SExp.py
+++ b/clvm/SExp.py
@@ -117,6 +117,9 @@ def to_sexp_type(
     return stack[0]
 
 
+_T_SExp = typing.TypeVar("_T_SExp")
+
+
 class SExp:
     """
     SExp provides higher level API on top of any object implementing the CLVM
@@ -173,7 +176,7 @@ def as_bin(self):
         return f.getvalue()
 
     @classmethod
-    def to(class_, v: CastableType) -> "SExp":
+    def to(class_: typing.Type[_T_SExp], v: CastableType) -> _T_SExp:
         if isinstance(v, class_):
             return v
 
diff --git a/clvm/py.typed b/clvm/py.typed
new file mode 100644
index 00000000..e69de29b
diff --git a/setup.py b/setup.py
index a1a86be7..568e3750 100755
--- a/setup.py
+++ b/setup.py
@@ -17,6 +17,9 @@
 setup(
     name="clvm",
     packages=["clvm",],
+    package_data={
+        "": ["py.typed"],
+    },
     author="Chia Network, Inc.",
     author_email="hello@chia.net",
     url="https://github.com/Chia-Network/clvm",