diff -Nrua old/src/SDL/i_video.c src/src/SDL/i_video.c
--- old/src/SDL/i_video.c	2009-11-09 17:22:06.000000000 +0100
+++ src/src/SDL/i_video.c	2009-11-09 17:23:13.000000000 +0100
@@ -412,7 +412,10 @@
     I_UploadNewPalette(newpal);
     newpal = NO_PALETTE_CHANGE;
   }
-  SDL_Flip(screen);
+  if (use_doublebuffer)
+    SDL_Flip(screen);
+  else
+    SDL_UpdateRect(screen, 0, 0, 0, 0);
 }
 
 //