diff --git a/hw/display/cg3.c b/hw/display/cg3.c
index 7d436945e94e2a6df7e45ba97f5933bc581587d9..b42f60e201159a2841d632e32504915d574038aa 100644
--- a/hw/display/cg3.c
+++ b/hw/display/cg3.c
@@ -114,7 +114,7 @@ static void cg3_update_display(void *opaque)
         int update = s->full_update;
 
         page = y * width;
-        update |= memory_region_get_dirty(&s->vram_mem, page, page + width,
+        update |= memory_region_get_dirty(&s->vram_mem, page, width,
                                           DIRTY_MEMORY_VGA);
         if (update) {
             if (y_start < 0) {