diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index ec5684b1d09502..6f25f91c0ff28d 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -236,7 +236,7 @@ static inline PyObject *get_interned_dict(PyInterpreterState *interp)
 }
 
 Py_ssize_t
-_PyUnicode_InternedSize()
+_PyUnicode_InternedSize(void)
 {
     return PyObject_Length(get_interned_dict(_PyInterpreterState_GET()));
 }