diff --git a/lib/compass/sass_extensions/sprites/layout_methods.rb b/lib/compass/sass_extensions/sprites/layout_methods.rb
index 60da675c..258328ac 100644
--- a/lib/compass/sass_extensions/sprites/layout_methods.rb
+++ b/lib/compass/sass_extensions/sprites/layout_methods.rb
@@ -100,11 +100,11 @@ module Compass
         end
         
         def height_for_horizontal_layout
-          @height = @images.map {|image| image.height + image.spacing}.max
+          @height = @images.map {|image| image.height + image.offset}.max
         end
         
         def width_for_horizontal_layout
-          @images.inject(0) { |sum, image| sum += (image.width + image.offset) }
+          @images.inject(0) { |sum, image| sum += (image.width + image.spacing) }
         end
         
         def width_for_vertical_layout
diff --git a/test/units/sprites/sprite_map_test.rb b/test/units/sprites/sprite_map_test.rb
index b9f4a0ef..8360b086 100644
--- a/test/units/sprites/sprite_map_test.rb
+++ b/test/units/sprites/sprite_map_test.rb
@@ -154,6 +154,7 @@ class SpriteMapTest < Test::Unit::TestCase
     base = horizontal("spacing" => Sass::Script::Number.new(10, ['px']))
     assert_equal [0, 20, 40, 60], base.images.map(&:left)
     assert_equal [0, 0, 0, 0], base.images.map(&:top)
+    assert_equal 80, base.width
   end
   
   it "should layout horizontaly with position" do