diff --git a/PC/winreg.c b/PC/winreg.c
index 28b316ae2f4..5469fcba044 100644
--- a/PC/winreg.c
+++ b/PC/winreg.c
@@ -1614,7 +1614,7 @@ winreg_SetValue_impl(PyObject *module, HKEY key, const Py_UNICODE *sub_key,
     }
 
     Py_BEGIN_ALLOW_THREADS
-    rc = RegSetValueW(key, sub_key, REG_SZ, value, value_length+1);
+    rc = RegSetValueW(key, sub_key, REG_SZ, value, (DWORD)(value_length + 1));
     Py_END_ALLOW_THREADS
     if (rc != ERROR_SUCCESS)
         return PyErr_SetFromWindowsErrWithFunction(rc, "RegSetValue");