diff --git a/ChangeLog b/ChangeLog
index c4b5d333a1..b6f09293b0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Sep 29 22:54:29 2008  Tadayoshi Funaba  <tadf@dotrb.org>
+
+	* lib/mathn.rb: added String#to_[rc].
+
 Mon Sep 29 20:41:19 2008  Tanaka Akira  <akr@fsij.org>
 
 	* string.c (rb_str_subseq): use rb_str_drop_bytes if possible.
diff --git a/lib/mathn.rb b/lib/mathn.rb
index 486d487296..b8d9f35465 100644
--- a/lib/mathn.rb
+++ b/lib/mathn.rb
@@ -61,6 +61,8 @@ class Fixnum
   remove_method :/
   alias / quo
 
+  def_canon *(instance_methods - Object.methods - [:canon])
+
   alias power! **
 
   def ** (other)
@@ -71,14 +73,14 @@ class Fixnum
     end
   end
 
-  def_canon *(instance_methods - Object.methods - [:canon])
-
 end
 
 class Bignum
   remove_method :/
   alias / quo
 
+  def_canon *(instance_methods - Object.methods - [:canon])
+
   alias power! **
 
   def ** (other)
@@ -89,8 +91,6 @@ class Bignum
     end
   end
 
-  def_canon *(instance_methods - Object.methods - [:canon])
-
 end
 
 alias RationalOrig Rational
@@ -277,6 +277,18 @@ class Integer
 
 end
 
+class String
+
+  alias to_r_orig to_r
+  private :to_r_orig
+  def to_r() to_r_orig.__send__(:canon) end
+
+  alias to_c_orig to_c
+  private :to_c_orig
+  def to_c() to_c_orig.__send__(:canon) end
+
+end
+
 class Float
 
   def_canon *(instance_methods - Object.methods - [:canon])