diff --git a/lib/sass/constant/color.rb b/lib/sass/constant/color.rb
index 65fe58d6..f827702c 100644
--- a/lib/sass/constant/color.rb
+++ b/lib/sass/constant/color.rb
@@ -1,17 +1,16 @@
 require 'sass/constant/literal'
 
 module Sass::Constant
-  class Color
-    include Literal
+  class Color < Literal
   
     REGEXP = /\##{"([0-9a-f]{1,2})" * 3}/
   
-    def initialize(value)
-      @red, @green, @blue = value.scan(REGEXP)[0].map { |num| num.ljust(2, 'f').to_i(16) }
+    def parse(value)
+      @value = value.scan(REGEXP)[0].map { |num| num.ljust(2, 'f').to_i(16) }
     end
     
     def to_s
-      red, green, blue = [@red, @green, @blue].map { |num| num.to_s(16).rjust(2, '0') }
+      red, green, blue = @value.map { |num| num.to_s(16).rjust(2, '0') }
       "##{red}#{green}#{blue}"
     end
   end
diff --git a/lib/sass/constant/literal.rb b/lib/sass/constant/literal.rb
index 2fc52f50..46a735a1 100644
--- a/lib/sass/constant/literal.rb
+++ b/lib/sass/constant/literal.rb
@@ -1,10 +1,10 @@
-module Sass::Constant; module Literal; end; end; # Let the subclasses see the superclass
+module Sass::Constant; class Literal; end; end; # Let the subclasses see the superclass
 
 require 'sass/constant/string'
 require 'sass/constant/number'
 require 'sass/constant/color'
 
-module Sass::Constant::Literal
+class Sass::Constant::Literal
   # The regular expression matching numbers.
   NUMBER  = /^[0-9]*\.?[0-9]+$/
 
@@ -22,7 +22,20 @@ module Sass::Constant::Literal
     end
   end
   
+  def initialize(value = nil)
+    self.parse(value) if value
+  end
+  
   def perform
     self
   end
+  
+  protected
+  
+  attr_reader :value
+  
+  def self.from_value(value)
+    instance = self.new
+    instance.instance_variable_set('@value', value)
+  end
 end
diff --git a/lib/sass/constant/number.rb b/lib/sass/constant/number.rb
index aa8bb275..089fbe3e 100644
--- a/lib/sass/constant/number.rb
+++ b/lib/sass/constant/number.rb
@@ -1,15 +1,18 @@
 require 'sass/constant/literal'
 
 module Sass::Constant
-  class Number
-    include Literal
+  class Number < Literal
   
-    def initialize(value)
+    def parse(value)
       value = value.to_f
       value = value.to_i if value % 1 == 0.0
       @value = value
     end
     
+    def plus(other)
+      Number.from_value(self.value + other.value)
+    end
+    
     def to_s
       @value.to_s
     end
diff --git a/lib/sass/constant/operation.rb b/lib/sass/constant/operation.rb
index 87b843b9..c89575a5 100644
--- a/lib/sass/constant/operation.rb
+++ b/lib/sass/constant/operation.rb
@@ -21,10 +21,14 @@ module Sass::Constant
       literal2 = @operand2.perform
       begin
         literal1.send(@operator, literal2)
-      rescue NoMethodError
+      rescue NoMethodError => e
+        raise e unless e.name == @operator
+        
         begin
           literal2.send(@operator, literal1)
-        rescue NoMethodError
+        rescue NoMethodError => e
+          raise e unless e.name == @operator
+        
           raise "Undefined operation:\n#{literal1} #{@operator} #{literal2}\n"
         end
       end
diff --git a/lib/sass/constant/string.rb b/lib/sass/constant/string.rb
index 88876e09..141b2b17 100644
--- a/lib/sass/constant/string.rb
+++ b/lib/sass/constant/string.rb
@@ -1,10 +1,9 @@
 require 'sass/constant/literal'
 
 module Sass::Constant
-  class String
-    include Literal
+  class String < Literal
     
-    def initialize(value)
+    def parse(value)
       @value = value
     end
     
diff --git a/test/sass/results/constants.css b/test/sass/results/constants.css
index 2a2e8719..35b7592f 100644
--- a/test/sass/results/constants.css
+++ b/test/sass/results/constants.css
@@ -1,2 +1,2 @@
-#main { width: 500px; background-color: #000; color: #ffffaf; }
+#main { width: 30; background-color: #000; color: #ffffaf; }
 #main #sidebar { background-color: #00ff98; num-normal: 10; num-dec: 10.2; num-dec0: 99; num-neg: -10; esc: 10+12; }
diff --git a/test/sass/templates/constants.sass b/test/sass/templates/constants.sass
index c383cd8c..9ea61754 100644
--- a/test/sass/templates/constants.sass
+++ b/test/sass/templates/constants.sass
@@ -1,4 +1,4 @@
-!width = 500px
+!width = 10 + 20
 !color = #00ff98
 !main_text = #ffa
 !num = 10