diff --git a/lib/aviator/string.rb b/lib/aviator/string.rb
index 7efa2e1..25d24b6 100644
--- a/lib/aviator/string.rb
+++ b/lib/aviator/string.rb
@@ -1,18 +1,24 @@
 class String
 
-  def camelize
-    word = self.slice(0,1).capitalize + self.slice(1..-1)
-    word.gsub(/_([a-zA-Z\d])/) { "#{$1.capitalize}" }
-  end
-
-  def constantize
-    self.split("::").inject(Object) do |namespace, sym|
-      namespace.const_get(sym.to_s.camelize, false)
+  unless instance_methods.include? 'camelize'
+    define_method :camelize do
+      word = self.slice(0,1).capitalize + self.slice(1..-1)
+      word.gsub(/_([a-zA-Z\d])/) { "#{$1.capitalize}" }
     end
   end
 
-  def underscore
-    self.gsub(/([a-z\d])([A-Z])/, '\1_\2').downcase
+  unless instance_methods.include? 'constantize'
+    define_method :constantize do
+      self.split("::").inject(Object) do |namespace, sym|
+        namespace.const_get(sym.to_s.camelize, false)
+      end
+    end
+  end
+
+  unless instance_methods.include? 'underscore'
+    define_method :underscore do
+      self.gsub(/([a-z\d])([A-Z])/, '\1_\2').downcase
+    end
   end
 
 end