overlay two images in android to set an imageview

I am trying to overlay two images in my app, but they seem to crash at my canvas.setBitmap() line. What am I doing wrong?

private void test() {
    Bitmap mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.t);
    Bitmap mBitmap2 = BitmapFactory.decodeResource(getResources(), R.drawable.tt);
    Bitmap bmOverlay = Bitmap.createBitmap(mBitmap.getWidth(), mBitmap.getHeight(), mBitmap.getConfig());
    Canvas canvas = new Canvas();
    canvas.setBitmap(bmOverlay);
    canvas.drawBitmap(mBitmap, new Matrix(), null);
    canvas.drawBitmap(mBitmap2, new Matrix(), null);
    testimage.setImageBitmap(bmOverlay);
}