diff --git a/src/ifcopenshell-python/ifcopenshell/entity_instance.py b/src/ifcopenshell-python/ifcopenshell/entity_instance.py
index fe7608de0b..46fef0a37f 100644
--- a/src/ifcopenshell-python/ifcopenshell/entity_instance.py
+++ b/src/ifcopenshell-python/ifcopenshell/entity_instance.py
@@ -409,9 +409,9 @@ class entity_instance:
     @overload
     def is_a(self) -> str: ...
     @overload
-    def is_a(self, ifc_class: str) -> bool: ...
+    def is_a(self, ifc_class: str, /) -> bool: ...
     @overload
-    def is_a(self, with_schema: bool) -> str: ...
+    def is_a(self, with_schema: bool, /) -> str: ...
     def is_a(self, *args: Union[str, bool]) -> Union[str, bool]:
         """Return the IFC class name of an instance, or checks if an instance belongs to a class.
 
diff --git a/ty.py b/ty.py
new file mode 100644
index 0000000000..10c33ee524
--- /dev/null
+++ b/ty.py
@@ -0,0 +1,12 @@
+from typing import Union, overload
+
+
+class entity_instance:
+    @overload
+    def is_a(self) -> str: ...
+    @overload
+    def is_a(self, ifc_class: str, /) -> bool: ...
+    @overload
+    def is_a(self, with_schema: bool, /) -> str: ...
+    def is_a(self, *args: Union[str, bool]) -> Union[str, bool]:
+        return args[0] if args else "foo"