Index: subsystems/win32/win32k/objects/bitmaps.c
===================================================================
--- subsystems/win32/win32k/objects/bitmaps.c	(revision 50894)
+++ subsystems/win32/win32k/objects/bitmaps.c	(working copy)
@@ -920,7 +920,8 @@
             pds->dsBmih.biHeight = pds->dsBm.bmHeight;
             pds->dsBmih.biPlanes = pds->dsBm.bmPlanes;
             pds->dsBmih.biBitCount = pds->dsBm.bmBitsPixel;
-			if(psurf->ppal->flFlags & PAL_BITFIELDS)
+            /* BI_BITFIELDS is only valid for 32 and 16 bits bitmaps, but PAL_BITFIELDS is used in 24 bits bitmaps too */
+			if((psurf->ppal->flFlags & PAL_BITFIELDS) && (psurf->SurfObj.iBitmapFormat == BMF_32BPP || psurf->SurfObj.iBitmapFormat == BMF_16BPP))
 			{
 				pds->dsBmih.biCompression = BI_BITFIELDS;
 			}
@@ -948,6 +949,8 @@
 					case BMF_PNG:
 					   pds->dsBmih.biCompression = BI_PNG;
 					   break;
+                    default:
+                        assert(FALSE); /* this shouldn't happen */
 				}
 			}
             pds->dsBmih.biSizeImage = psurf->SurfObj.cjBits;