How to remove minimize and maximize buttons from a resizable window?

I’ve stolen some code I found on the MSDN forums and made an extension method on the Window class, like this:

internal static class WindowExtensions
{
    // from winuser.h
    private const int GWL_STYLE      = -16,
                      WS_MAXIMIZEBOX = 0x10000,
                      WS_MINIMIZEBOX = 0x20000;

    [DllImport("user32.dll")]
    extern private static int GetWindowLong(IntPtr hwnd, int index);

    [DllImport("user32.dll")]
    extern private static int SetWindowLong(IntPtr hwnd, int index, int value);

    internal static void HideMinimizeAndMaximizeButtons(this Window window)
    {
        IntPtr hwnd = new System.Windows.Interop.WindowInteropHelper(window).Handle;
        var currentStyle = GetWindowLong(hwnd, GWL_STYLE);

        SetWindowLong(hwnd, GWL_STYLE, (currentStyle & ~WS_MAXIMIZEBOX & ~WS_MINIMIZEBOX));
    }
}

The only other thing to remember is that for some reason this doesn’t work from a window’s constructor. I got around that by chucking this into the constructor:

this.SourceInitialized += (x, y) =>
{
    this.HideMinimizeAndMaximizeButtons();
};