Index: dll/win32/user32/windows/bitmap.c
===================================================================
--- dll/win32/user32/windows/bitmap.c	(revision 39857)
+++ dll/win32/user32/windows/bitmap.c	(working copy)
@@ -462,6 +462,12 @@
          ColorCount = 1 << BitmapInfo->bmiHeader.biBitCount;
       HeaderSize = sizeof(BITMAPINFOHEADER) + ColorCount * sizeof(RGBQUAD);
    }
+
+   if (BitmapInfo->bmiHeader.biCompression == BI_BITFIELDS)
+   {
+      HeaderSize += 3 * sizeof(RGBQUAD);
+   }
+
    Data = (PVOID)((ULONG_PTR)BitmapInfo + HeaderSize);
 
    PrivateInfo = RtlAllocateHeap(GetProcessHeap(), 0, HeaderSize);