diff --git a/src/vga.js b/src/vga.js
index bff80159..3d6568fe 100644
--- a/src/vga.js
+++ b/src/vga.js
@@ -2280,7 +2280,7 @@ VGAScreen.prototype.screen_fill_buffer = function()
     if(this.svga_enabled)
     {
         let min_y = 0;
-        let max_y = this.svga_height - 1;
+        let max_y = this.svga_height;
 
         if(this.svga_bpp === 8)
         {
@@ -2300,19 +2300,21 @@ VGAScreen.prototype.screen_fill_buffer = function()
             this.cpu.svga_fill_pixel_buffer(this.svga_bpp, this.svga_offset);
 
             const bytes_per_pixel = this.svga_bpp === 15 ? 2 : this.svga_bpp / 8;
-            const bytes_per_line = bytes_per_pixel * this.svga_width;
-            min_y = this.cpu.svga_dirty_bitmap_min_offset[0] / bytes_per_line | 0;
-            max_y = this.cpu.svga_dirty_bitmap_max_offset[0] / bytes_per_line | 0;
+            min_y = ((this.cpu.svga_dirty_bitmap_min_offset[0] / bytes_per_pixel | 0) - this.svga_offset) / this.svga_width;
+            max_y = ((this.cpu.svga_dirty_bitmap_max_offset[0] / bytes_per_pixel | 0) - this.svga_offset) / this.svga_width + 1;
         }
 
         if(min_y < max_y)
         {
+            min_y = Math.max(min_y, 0);
+            max_y = Math.min(max_y, this.svga_height);
+
             this.bus.send("screen-fill-buffer-end", [{
                 image_data: this.image_data,
                 screen_x: 0, screen_y: min_y,
                 buffer_x: 0, buffer_y: min_y,
                 buffer_width: this.svga_width,
-                buffer_height: max_y - min_y + 1,
+                buffer_height: max_y - min_y,
             }]);
         }
     }