diff --git a/Include/internal/pycore_unionobject.h b/Include/internal/pycore_unionobject.h
index 4101537926a..b36d206b15c 100644
--- a/Include/internal/pycore_unionobject.h
+++ b/Include/internal/pycore_unionobject.h
@@ -8,7 +8,7 @@ extern "C" {
 #  error "this header requires Py_BUILD_CORE define"
 #endif
 
-extern PyTypeObject _PyUnion_Type;
+PyAPI_DATA(PyTypeObject) _PyUnion_Type;
 #define _PyUnion_Check(op) Py_IS_TYPE((op), &_PyUnion_Type)
 PyAPI_FUNC(PyObject *) _Py_union_type_or(PyObject *, PyObject *);