diff --git a/platform/android/surface.rs b/platform/android/surface.rs
index c0777df..80f525f 100644
--- a/platform/android/surface.rs
+++ b/platform/android/surface.rs
@@ -52,8 +52,8 @@ impl NativeCompositingGraphicsContext {
 }
 
 pub struct NativeSurface {
-    image: Option<EGLImageKHR>,
-    bitmap: *c_void,
+    image: Option<EGLImageKHR>, // For GPU rendering
+    bitmap: Option<Vec<u8>>, // For CPU rendering
     will_leak: bool,
 }
 
@@ -65,7 +65,7 @@ impl NativeSurface {
         }
         NativeSurface {
             image : _image,
-            bitmap : ptr::null(),
+            bitmap: None,
             will_leak: true,
         }
     }
@@ -74,15 +74,13 @@ impl NativeSurface {
 impl NativeSurfaceMethods for NativeSurface {
     /// This may only be called on the case of CPU rendering.
     fn new(_native_context: &NativePaintingGraphicsContext, size: Size2D<i32>, _stride: i32) -> NativeSurface {
-        unsafe {
-            let len = size.width * size.height * 4;
-            let bitmap: Vec<u8> = Vec::from_elem(len as uint, 0 as u8);
-
-            NativeSurface {
-                image: None,
-                bitmap: mem::transmute(bitmap.as_ptr()),
-                will_leak : true,
-            }
+        let len = size.width * size.height * 4;
+        let bitmap: Vec<u8> = Vec::from_elem(len as uint, 0 as u8);
+
+        NativeSurface {
+            image: None,
+            bitmap: Some(bitmap),
+            will_leak : true,
         }
     }
 
@@ -92,32 +90,34 @@ impl NativeSurfaceMethods for NativeSurface {
                        texture: &Texture,
                        _size: Size2D<int>) {
         let _bound = texture.bind();
-
-        unsafe {
-            match self.image {
-                None => {
-                    if self.bitmap != ptr::null() {
-                        glTexImage2D(TEXTURE_2D, 0, BGRA as i32, _size.width as i32, _size.height as i32, 0, BGRA as u32, UNSIGNED_BYTE, self.bitmap);
-                    }
-                    else {
-                        debug!("Cannot bind the buffer(CPU rendering), there is no bitmap");
+        match self.image {
+            None => match self.bitmap {
+                Some(ref bitmap) => {
+                    let data = bitmap.as_ptr() as *c_void;
+                    unsafe {
+                        glTexImage2D(TEXTURE_2D, 0, BGRA as i32, _size.width as i32, _size.height as i32,
+                                     0, BGRA as u32, UNSIGNED_BYTE, data);
                     }
-                },
-                Some(image_khr) => {
-                    egl_image_target_texture2d_oes(TEXTURE_2D, image_khr);
                 }
+                None => {
+                    debug!("Cannot bind the buffer(CPU rendering), there is no bitmap");
+                }
+            },
+            Some(image_khr) => {
+                egl_image_target_texture2d_oes(TEXTURE_2D, image_khr);
             }
         }
     }
 
     /// This may only be called on the painting side.
-    fn upload(&self, _graphics_context: &NativePaintingGraphicsContext, data: &[u8]) {
-        unsafe {
-            if self.bitmap != ptr::null() {
-                let dest:&mut [u8] = mem::transmute((self.bitmap, data.len()));
-                dest.copy_memory(data);
+    fn upload(&mut self, _graphics_context: &NativePaintingGraphicsContext, data: &[u8]) {
+        match self.bitmap {
+            Some(ref mut bitmap) => {
+                unsafe {
+                    bitmap.as_mut_slice().copy_memory(data);
+                }
             }
-            else {
+            None => {
                 debug!("Cannot upload the buffer(CPU rendering), there is no bitmap");
             }
         }
diff --git a/platform/linux/surface.rs b/platform/linux/surface.rs
index d19a3bd..f858c1a 100644
--- a/platform/linux/surface.rs
+++ b/platform/linux/surface.rs
@@ -266,7 +266,7 @@ impl NativeSurfaceMethods for NativeSurface {
     }
 
     /// This may only be called on the painting side.
-    fn upload(&self, graphics_context: &NativePaintingGraphicsContext, data: &[u8]) {
+    fn upload(&mut self, graphics_context: &NativePaintingGraphicsContext, data: &[u8]) {
         unsafe {
             // Ensure that we're running on the render task. Take the display.
             let pixmap = self.pixmap;
diff --git a/platform/macos/surface.rs b/platform/macos/surface.rs
index fcd118b..2f1dd5a 100644
--- a/platform/macos/surface.rs
+++ b/platform/macos/surface.rs
@@ -206,7 +206,7 @@ impl NativeSurfaceMethods for NativeSurface {
         io_surface.bind_to_gl_texture(size)
     }
 
-    fn upload(&self, _: &NativePaintingGraphicsContext, data: &[u8]) {
+    fn upload(&mut self, _: &NativePaintingGraphicsContext, data: &[u8]) {
         let io_surface = io_surface::lookup(self.io_surface_id.unwrap());
         io_surface.upload(data)
     }
diff --git a/platform/surface.rs b/platform/surface.rs
index 0397a77..7672127 100644
--- a/platform/surface.rs
+++ b/platform/surface.rs
@@ -54,7 +54,7 @@ pub trait NativeSurfaceMethods {
                        size: Size2D<int>);
 
     /// Uploads pixel data to the surface. Painting task only.
-    fn upload(&self, native_context: &NativePaintingGraphicsContext, data: &[u8]);
+    fn upload(&mut self, native_context: &NativePaintingGraphicsContext, data: &[u8]);
 
     /// Returns an opaque ID identifying the surface for debugging.
     fn get_id(&self) -> int;