diff --git a/src/cpu.js b/src/cpu.js
index 3e7b0005..9cb5c6d4 100644
--- a/src/cpu.js
+++ b/src/cpu.js
@@ -161,6 +161,9 @@ function CPU(bus, wm, next_tick_immediately)
 
     this.reg_pdpte = v86util.view(Int32Array, memory, 968, 8);
 
+    this.svga_dirty_bitmap_min_offset = v86util.view(Uint32Array, memory, 716, 1);
+    this.svga_dirty_bitmap_max_offset = v86util.view(Uint32Array, memory, 720, 1);
+
     this.fw_value = [];
     this.fw_pointer = 0;
     this.option_roms = [];
diff --git a/src/rust/cpu/global_pointers.rs b/src/rust/cpu/global_pointers.rs
index e884b4c5..00b0b336 100644
--- a/src/rust/cpu/global_pointers.rs
+++ b/src/rust/cpu/global_pointers.rs
@@ -40,6 +40,10 @@ pub const instruction_counter: *mut u32 = 664 as *mut u32;
 pub const sreg: *mut u16 = 668 as *mut u16;
 pub const dreg: *mut i32 = 684 as *mut i32;
 
+// filled in by svga_fill_pixel_buffer, read by javacsript for optimised putImageData calls
+pub const svga_dirty_bitmap_min_offset: *mut u32 = 716 as *mut u32;
+pub const svga_dirty_bitmap_max_offset: *mut u32 = 720 as *mut u32;
+
 pub const segment_is_null: *mut bool = 724 as *mut bool;
 pub const segment_offsets: *mut i32 = 736 as *mut i32;
 pub const segment_limits: *mut u32 = 768 as *mut u32;
diff --git a/src/rust/cpu/vga.rs b/src/rust/cpu/vga.rs
index a78fbeb7..5c7e56a0 100644
--- a/src/rust/cpu/vga.rs
+++ b/src/rust/cpu/vga.rs
@@ -1,5 +1,6 @@
 #![allow(non_upper_case_globals)]
 
+use cpu::global_pointers;
 use cpu::memory;
 
 pub static mut dirty_bitmap: Vec<u64> = Vec::new();
@@ -26,6 +27,9 @@ pub unsafe fn svga_mark_dirty() {
 }
 
 fn iter_dirty_pages(f: &dyn Fn(isize)) {
+    let mut min_off = u32::MAX;
+    let mut max_off = u32::MIN;
+
     for (i, &word) in unsafe { &dirty_bitmap }.iter().enumerate() {
         if word == 0 {
             continue;
@@ -36,13 +40,22 @@ fn iter_dirty_pages(f: &dyn Fn(isize)) {
             }
             let off = ((i << 6 | j) << 12) as isize;
             dbg_assert!(off < unsafe { memory::vga_memory_size as isize });
+            if min_off == u32::MAX {
+                min_off = off as u32;
+            }
+            max_off = off as u32;
             f(off);
         }
     }
+
+    unsafe {
+        *global_pointers::svga_dirty_bitmap_min_offset = min_off;
+        *global_pointers::svga_dirty_bitmap_max_offset = max_off;
+    }
 }
 
 #[no_mangle]
-pub unsafe fn svga_fill_pixel_buffer(bpp: i32, svga_dest_offset: i32) {
+pub unsafe fn svga_fill_pixel_buffer(bpp: u32, svga_dest_offset: u32) {
     let debug_bounds = false;
 
     match bpp {
@@ -58,6 +71,8 @@ pub unsafe fn svga_fill_pixel_buffer(bpp: i32, svga_dest_offset: i32) {
                 isize::min(1024, dest_buffer.len() as isize - dest_offset)
             };
 
+            dbg_assert!(src as u32 % 8 == 0);
+            dbg_assert!(dest as u32 % 8 == 0);
             for i in 0..end {
                 dbg_assert!(off + i < memory::vga_memory_size as isize);
                 let dword = *src.offset(i);
diff --git a/src/vga.js b/src/vga.js
index b70865a7..bff80159 100644
--- a/src/vga.js
+++ b/src/vga.js
@@ -2279,6 +2279,9 @@ VGAScreen.prototype.screen_fill_buffer = function()
 
     if(this.svga_enabled)
     {
+        let min_y = 0;
+        let max_y = this.svga_height - 1;
+
         if(this.svga_bpp === 8)
         {
             // XXX: Slow, should be ported to rust, but it doesn't have access to vga256_palette
@@ -2295,18 +2298,23 @@ VGAScreen.prototype.screen_fill_buffer = function()
         else
         {
             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;
         }
 
-        const min_y = 0;
-        const 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,
-        }]);
+        if(min_y < max_y)
+        {
+            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,
+            }]);
+        }
     }
     else
     {