diff --git a/src/ocptv/output/emit.py b/src/ocptv/output/emit.py
index 4ad976e..005d672 100644
--- a/src/ocptv/output/emit.py
+++ b/src/ocptv/output/emit.py
@@ -16,7 +16,7 @@
 JSON = ty.Union[ty.Dict[str, "JSON"], ty.List["JSON"], Primitive]
 
 
-def _is_optional(field: ty.Type):
+def _is_optional(field: ty.Type) -> bool:
     # type hackery incoming
     # ty.Optional[T] == ty.Union[T, None]
     # since ty.Union[ty.Union[T,U]] = ty.Union[T,U] we can the
@@ -30,7 +30,7 @@ class ArtifactEmitter:
     Uses the low level dataclass models for the spec, but should not be used in user code.
     """
 
-    def __init__(self, writer: Writer):
+    def __init__(self, writer: Writer) -> None:
         self._seq_lock = threading.Lock()
         self._seq = 0
 
@@ -41,7 +41,7 @@ def __init__(self, writer: Writer):
         self._version_emitted = threading.Event()
 
     @staticmethod
-    def _serialize(artifact: ArtifactType):
+    def _serialize(artifact: ArtifactType) -> str:
         def visit(
             value: ty.Union[ArtifactType, ty.Dict, ty.List, Primitive],
             formatter: ty.Optional[ty.Callable[[ty.Any], str]] = None,
@@ -56,7 +56,7 @@ def visit(
                     val = getattr(value, field.name)
 
                     if val is None:
-                        if not _is_optional(field.type):
+                        if not _is_optional(ty.cast(ty.Type, field.type)):
                             # TODO: fix exception text/type
                             raise RuntimeError("unacceptable none where not optional")
 
diff --git a/src/ocptv/output/runtime_checks.py b/src/ocptv/output/runtime_checks.py
index c8f83d5..085f692 100644
--- a/src/ocptv/output/runtime_checks.py
+++ b/src/ocptv/output/runtime_checks.py
@@ -119,8 +119,8 @@ def __str__(self):
 
 
 def _check_type_any(obj: CheckedValue, hint: ty.Type, trace: ty.List[str]):
-    type_origin = get_origin(hint)
-    type_args = get_args(hint)
+    type_origin = ty.cast(ty.Type | None, get_origin(hint))
+    type_args = ty.cast(ty.Tuple[ty.Type, ...], get_args(hint))
 
     if type_origin is list:
         # generic type: typ == ty.List[...]
@@ -186,7 +186,7 @@ def _check_type_any(obj: CheckedValue, hint: ty.Type, trace: ty.List[str]):
     elif dc.is_dataclass(obj):
         for field in dc.fields(obj):
             subtrace = trace + [f"{obj.__class__.__name__}.{field.name}"]
-            _check_type_any(getattr(obj, field.name), field.type, subtrace)
+            _check_type_any(getattr(obj, field.name), ty.cast(ty.Type, field.type), subtrace)
 
     elif not isinstance(obj, hint):
         raise TypeCheckError(obj, expected=hint.__name__, trace=trace)