diff --git a/doc-src/lib/stylesheets/sass_extensions.rb b/doc-src/lib/stylesheets/sass_extensions.rb
index 8e96b30c..b97e26d4 100644
--- a/doc-src/lib/stylesheets/sass_extensions.rb
+++ b/doc-src/lib/stylesheets/sass_extensions.rb
@@ -253,11 +253,13 @@ module Sass
       end
     end
     class UnaryOperation < Node
-      OPERATORS_TO_SASS = {
-        :minus => "-",
-        :div   => "/",
-        :not   => "not "
-      }
+      unless defined? OPERATORS_TO_SASS
+        OPERATORS_TO_SASS = {
+          :minus => "-",
+          :div   => "/",
+          :not   => "not "
+        }
+      end
       def to_sass(format = :text)
         "#{OPERATORS_TO_SASS[@operator]}#{@operand.to_sass}"
       end
@@ -268,4 +270,4 @@ module Sass
       end
     end
   end
-end
\ No newline at end of file
+end