diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c
index 326d511e60..a9f6d5bb4c 100644
--- a/hw/display/cirrus_vga.c
+++ b/hw/display/cirrus_vga.c
@@ -667,11 +667,11 @@ static void cirrus_invalidate_region(CirrusVGAState * s, int off_begin,
     }
 
     for (y = 0; y < lines; y++) {
-	off_cur = off_begin;
-	off_cur_end = (off_cur + bytesperline) & s->cirrus_addr_mask;
+        off_cur = off_begin;
+        off_cur_end = ((off_cur + bytesperline - 1) & s->cirrus_addr_mask) + 1;
         assert(off_cur_end >= off_cur);
         memory_region_set_dirty(&s->vga.vram, off_cur, off_cur_end - off_cur);
-	off_begin += off_pitch;
+        off_begin += off_pitch;
     }
 }