diff --git a/win/win32/mhmain.c b/win/win32/mhmain.c
index 2b52f71cf..48c2ea3a6 100644
--- a/win/win32/mhmain.c
+++ b/win/win32/mhmain.c
@@ -370,7 +370,7 @@ MainWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
             ZeroMemory(kbd_state, sizeof(kbd_state));
             GetKeyboardState(kbd_state);
 
-            if (ToAscii(wParam, (lParam >> 16) & 0xFF, kbd_state, &c, 0)) {
+            if (ToAscii((UINT) wParam, (lParam >> 16) & 0xFF, kbd_state, &c, 0)) {
                 NHEVENT_KBD(c & 0xFF);
                 return 0;
             } else {