diff --git a/lib/compass/sass_extensions/functions/urls.rb b/lib/compass/sass_extensions/functions/urls.rb
index 581a080a..f72cdeb0 100644
--- a/lib/compass/sass_extensions/functions/urls.rb
+++ b/lib/compass/sass_extensions/functions/urls.rb
@@ -1,167 +1,203 @@
 module Compass::SassExtensions::Functions::Urls
 
-  def stylesheet_url(path, only_path = Sass::Script::Bool.new(false))
-    # Compute the path to the stylesheet, either root relative or stylesheet relative
-    # or nil if the http_stylesheets_path is not set in the configuration.
-    http_stylesheets_path = if relative?
-      compute_relative_path(Compass.configuration.css_path)
-    elsif Compass.configuration.http_stylesheets_path
-      Compass.configuration.http_stylesheets_path
-    else
-      Compass.configuration.http_root_relative(Compass.configuration.css_dir)
-    end
 
-    path = "#{http_stylesheets_path}/#{path.value}"
-    if only_path.to_bool
-      Sass::Script::String.new(clean_path(path))
-    else
-      clean_url(path)
-    end
+  def self.has?(base, instance_method)
+    Sass::Util.has?(:instance_method, base, instance_method)
   end
-  Sass::Script::Functions.declare :stylesheet_url, [:path]
-  Sass::Script::Functions.declare :stylesheet_url, [:path, :only_path]
 
-  def font_url(path, only_path = Sass::Script::Bool.new(false))
-    path = path.value # get to the string value of the literal.
-
-    # Short curcuit if they have provided an absolute url.
-    if absolute_path?(path)
-      return Sass::Script::String.new("url(#{path})")
-    end
-
-    # Compute the path to the font file, either root relative or stylesheet relative
-    # or nil if the http_fonts_path cannot be determined from the configuration.
-    http_fonts_path = if relative?
-                        compute_relative_path(Compass.configuration.fonts_path)
-                      else
-                        Compass.configuration.http_fonts_path
-                      end
-
-    path = "#{http_fonts_path}/#{path}"
-
-    if only_path.to_bool
-      Sass::Script::String.new(clean_path(path))
-    else
-      clean_url(path)
-    end
+  def self.included(base)
+    base.send(:include, StylesheetUrl) unless has?(base, :stylesheet_url)
+    base.send(:include, FontUrl) unless has?(base, :font_url)
+    base.send(:include, ImageUrl) unless has?(base, :image_url)
+    base.send(:include, GeneratedImageUrl) unless has?(base, :generated_image_url)
   end
-  Sass::Script::Functions.declare :font_url, [:path]
-  Sass::Script::Functions.declare :font_url, [:path, :only_path]
 
-  def image_url(path, only_path = Sass::Script::Bool.new(false), cache_buster = Sass::Script::Bool.new(true))
-    path = path.value # get to the string value of the literal.
-
-    if path =~ %r{^#{Regexp.escape(Compass.configuration.http_images_path)}/(.*)}
-      # Treat root relative urls (without a protocol) like normal if they start with
-      # the images path.
-      path = $1
-    elsif absolute_path?(path)
-      # Short curcuit if they have provided an absolute url.
-      return Sass::Script::String.new("url(#{path})")
-    end
-
-    # Compute the path to the image, either root relative or stylesheet relative
-    # or nil if the http_images_path is not set in the configuration.
-    http_images_path = if relative?
-      compute_relative_path(Compass.configuration.images_path)
-    elsif Compass.configuration.http_images_path
-      Compass.configuration.http_images_path
-    else
-      Compass.configuration.http_root_relative(Compass.configuration.images_dir)
-    end
-
-    # Compute the real path to the image on the file stystem if the images_dir is set.
-    real_path = if Compass.configuration.images_dir
-      File.join(Compass.configuration.project_path, Compass.configuration.images_dir, path)
-    end
-
-    # prepend the path to the image if there's one
-    if http_images_path
-      http_images_path = "#{http_images_path}/" unless http_images_path[-1..-1] == "/"
-      path = "#{http_images_path}#{path}"
-    end
-
-    # Compute the asset host unless in relative mode.
-    asset_host = if !relative? && Compass.configuration.asset_host
-      Compass.configuration.asset_host.call(path)
-    end
-
-    # Compute and append the cache buster if there is one.
-    if cache_buster.to_bool
-      if cache_buster.is_a?(Sass::Script::String)
-        path += "?#{cache_buster.value}"
-      else
-        path = cache_busted_path(path, real_path)
+  module StylesheetUrl
+    def self.included(base)
+      if base.respond_to?(:declare)
+        base.declare :stylesheet_url, [:path]
+        base.declare :stylesheet_url, [:path, :only_path]
       end
     end
+    def stylesheet_url(path, only_path = Sass::Script::Bool.new(false))
+      # Compute the path to the stylesheet, either root relative or stylesheet relative
+      # or nil if the http_images_path is not set in the configuration.
+      http_stylesheets_path = if relative?
+        compute_relative_path(Compass.configuration.css_path)
+      elsif Compass.configuration.http_stylesheets_path
+        Compass.configuration.http_stylesheets_path
+      else
+        Compass.configuration.http_root_relative(Compass.configuration.css_dir)
+      end
 
-    # prepend the asset host if there is one.
-    path = "#{asset_host}#{'/' unless path[0..0] == "/"}#{path}" if asset_host
+      path = "#{http_stylesheets_path}/#{path.value}"
+      if only_path.to_bool
+        Sass::Script::String.new(clean_path(path))
+      else
+        clean_url(path)
+      end
+    end
+  end
+
+  module FontUrl
+    def self.included(base)
+      if base.respond_to?(:declare)
+        base.declare :font_url,       [:path]
+        base.declare :font_url,       [:path, :only_path]
+      end
+    end
+    def font_url(path, only_path = Sass::Script::Bool.new(false))
+      path = path.value # get to the string value of the literal.
+
+      # Short curcuit if they have provided an absolute url.
+      if absolute_path?(path)
+        return Sass::Script::String.new("url(#{path})")
+      end
+
+      # Compute the path to the font file, either root relative or stylesheet relative
+      # or nil if the http_fonts_path cannot be determined from the configuration.
+      http_fonts_path = if relative?
+                          compute_relative_path(Compass.configuration.fonts_path)
+                        else
+                          Compass.configuration.http_fonts_path
+                        end
+
+      path = "#{http_fonts_path}/#{path}"
+
+      if only_path.to_bool
+        Sass::Script::String.new(clean_path(path))
+      else
+        clean_url(path)
+      end
+    end
+  end
+
+  module ImageUrl
+    def self.included(base)
+      if base.respond_to?(:declare)
+        base.declare :image_url,      [:path]
+        base.declare :image_url,      [:path, :only_path]
+        base.declare :image_url,      [:path, :only_path, :cache_buster]
+      end
+    end
+    def image_url(path, only_path = Sass::Script::Bool.new(false), cache_buster = Sass::Script::Bool.new(true))
+      path = path.value # get to the string value of the literal.
+
+      if path =~ %r{^#{Regexp.escape(Compass.configuration.http_images_path)}/(.*)}
+        # Treat root relative urls (without a protocol) like normal if they start with
+        # the images path.
+        path = $1
+      elsif absolute_path?(path)
+        # Short curcuit if they have provided an absolute url.
+        return Sass::Script::String.new("url(#{path})")
+      end
+
+      # Compute the path to the image, either root relative or stylesheet relative
+      # or nil if the http_images_path is not set in the configuration.
+      http_images_path = if relative?
+        compute_relative_path(Compass.configuration.images_path)
+      elsif Compass.configuration.http_images_path
+        Compass.configuration.http_images_path
+      else
+        Compass.configuration.http_root_relative(Compass.configuration.images_dir)
+      end
+
+      # Compute the real path to the image on the file stystem if the images_dir is set.
+      real_path = if Compass.configuration.images_dir
+        File.join(Compass.configuration.project_path, Compass.configuration.images_dir, path)
+      end
+
+      # prepend the path to the image if there's one
+      if http_images_path
+        http_images_path = "#{http_images_path}/" unless http_images_path[-1..-1] == "/"
+        path = "#{http_images_path}#{path}"
+      end
+
+      # Compute the asset host unless in relative mode.
+      asset_host = if !relative? && Compass.configuration.asset_host
+        Compass.configuration.asset_host.call(path)
+      end
+
+      # Compute and append the cache buster if there is one.
+      if cache_buster.to_bool
+        if cache_buster.is_a?(Sass::Script::String)
+          path += "?#{cache_buster.value}"
+        else
+          path = cache_busted_path(path, real_path)
+        end
+      end
+
+      # prepend the asset host if there is one.
+      path = "#{asset_host}#{'/' unless path[0..0] == "/"}#{path}" if asset_host
+
+      if only_path.to_bool
+        Sass::Script::String.new(clean_path(path))
+      else
+        clean_url(path)
+      end
+    end
+  end
+
+  module GeneratedImageUrl
+    def self.included(base)
+      if base.respond_to?(:declare)
+        base.declare :generated_image_url, [:path]
+        base.declare :generated_image_url, [:path, :cache_buster]
+      end
+    end
+    def generated_image_url(path, cache_buster = Sass::Script::Bool.new(false))
+      path = path.value # get to the string value of the literal.
+
+      if path =~ %r{^#{Regexp.escape(Compass.configuration.http_generated_images_path)}/(.*)}
+        # Treat root relative urls (without a protocol) like normal if they start with
+        # the generated_images path.
+        path = $1
+      elsif absolute_path?(path)
+        # Short curcuit if they have provided an absolute url.
+        return Sass::Script::String.new("url(#{path})")
+      end
+
+      # Compute the path to the image, either root relative or stylesheet relative
+      # or nil if the http_generated_images_path is not set in the configuration.
+      http_generated_images_path = if relative?
+        compute_relative_path(Compass.configuration.generated_images_path)
+      elsif Compass.configuration.http_generated_images_path
+        Compass.configuration.http_generated_images_path
+      else
+        Compass.configuration.http_root_relative(Compass.configuration.generated_images_dir)
+      end
+
+      # Compute the real path to the image on the file stystem if the generated_images_dir is set.
+      real_path = if Compass.configuration.generated_images_dir
+        File.join(Compass.configuration.project_path, Compass.configuration.generated_images_dir, path)
+      end
+
+      # prepend the path to the image if there's one
+      if http_generated_images_path
+        http_generated_images_path = "#{http_generated_images_path}/" unless http_generated_images_path[-1..-1] == "/"
+        path = "#{http_generated_images_path}#{path}"
+      end
+
+      # Compute the asset host unless in relative mode.
+      asset_host = if !relative? && Compass.configuration.asset_host
+        Compass.configuration.asset_host.call(path)
+      end
+
+      # Compute and append the cache buster if there is one.
+      if cache_buster.to_bool
+        if cache_buster.is_a?(Sass::Script::String)
+          path += "?#{cache_buster.value}"
+        else
+          path = cache_busted_path(path, real_path)
+        end
+      end
+
+      # prepend the asset host if there is one.
+      path = "#{asset_host}#{'/' unless path[0..0] == "/"}#{path}" if asset_host
 
-    if only_path.to_bool
-      Sass::Script::String.new(clean_path(path))
-    else
       clean_url(path)
     end
   end
-  Sass::Script::Functions.declare :image_url, [:path]
-  Sass::Script::Functions.declare :image_url, [:path, :only_path]
-  Sass::Script::Functions.declare :image_url, [:path, :only_path, :cache_buster]
-
-  def generated_image_url(path, cache_buster = Sass::Script::Bool.new(false))
-    path = path.value # get to the string value of the literal.
-
-    if path =~ %r{^#{Regexp.escape(Compass.configuration.http_generated_images_path)}/(.*)}
-      # Treat root relative urls (without a protocol) like normal if they start with
-      # the generated_images path.
-      path = $1
-    elsif absolute_path?(path)
-      # Short curcuit if they have provided an absolute url.
-      return Sass::Script::String.new("url(#{path})")
-    end
-
-    # Compute the path to the image, either root relative or stylesheet relative
-    # or nil if the http_generated_images_path is not set in the configuration.
-    http_generated_images_path = if relative?
-      compute_relative_path(Compass.configuration.generated_images_path)
-    elsif Compass.configuration.http_generated_images_path
-      Compass.configuration.http_generated_images_path
-    else
-      Compass.configuration.http_root_relative(Compass.configuration.generated_images_dir)
-    end
-
-    # Compute the real path to the image on the file stystem if the generated_images_dir is set.
-    real_path = if Compass.configuration.generated_images_dir
-      File.join(Compass.configuration.project_path, Compass.configuration.generated_images_dir, path)
-    end
-
-    # prepend the path to the image if there's one
-    if http_generated_images_path
-      http_generated_images_path = "#{http_generated_images_path}/" unless http_generated_images_path[-1..-1] == "/"
-      path = "#{http_generated_images_path}#{path}"
-    end
-
-    # Compute the asset host unless in relative mode.
-    asset_host = if !relative? && Compass.configuration.asset_host
-      Compass.configuration.asset_host.call(path)
-    end
-
-    # Compute and append the cache buster if there is one.
-    if cache_buster.to_bool
-      if cache_buster.is_a?(Sass::Script::String)
-        path += "?#{cache_buster.value}"
-      else
-        path = cache_busted_path(path, real_path)
-      end
-    end
-
-    # prepend the asset host if there is one.
-    path = "#{asset_host}#{'/' unless path[0..0] == "/"}#{path}" if asset_host
-
-    clean_url(path)
-  end
-  Sass::Script::Functions.declare :generated_image_url, [:path]
-  Sass::Script::Functions.declare :generated_image_url, [:path, :cache_buster]
 
   private
 
diff --git a/test/units/sass_extensions_test.rb b/test/units/sass_extensions_test.rb
index 8b8aeabd..372d54e6 100644
--- a/test/units/sass_extensions_test.rb
+++ b/test/units/sass_extensions_test.rb
@@ -98,6 +98,20 @@ class SassExtensionsTest < Test::Unit::TestCase
     assert_equal "true", evaluate("prefixed(-css2, css2-fallback(css3, css2))")
   end
 
+  %w(stylesheet_url font_url image_url generated_image_url).each do |helper|
+    class_eval %Q{
+      def test_#{helper}_helper_defers_to_existing_helper
+        c = Class.new do
+          def #{helper}(*args)
+            :original
+          end
+        end
+        c.send(:include, Compass::SassExtensions::Functions::Urls)
+        assert_equal :original, c.new.#{helper}("logo.png")
+      end
+    }
+  end
+
 protected
   def evaluate(value)
     Sass::Script::Parser.parse(value, 0, 0).perform(Sass::Environment.new).to_s