diff --git a/dlls/user.exe16/window.c b/dlls/user.exe16/window.c
index e81d9ace3ae..10f1389f0a7 100644
--- a/dlls/user.exe16/window.c
+++ b/dlls/user.exe16/window.c
@@ -1924,7 +1924,7 @@ HWND16 WINAPI CreateWindowEx16( DWORD exStyle, LPCSTR className,
     {
         WCHAR bufferW[256];
 
-        if (!MultiByteToWideChar( CP_ACP, 0, className, -1, bufferW, sizeof(bufferW)/sizeof(WCHAR) ))
+        if (!MultiByteToWideChar( CP_ACP, 0, className, -1, bufferW, ARRAY_SIZE(bufferW)))
             return 0;
         hwnd = create_window16( (CREATESTRUCTW *)&cs, bufferW, HINSTANCE_32(instance), FALSE );
     }