diff --git a/ChangeLog b/ChangeLog
index ae07f5b4fd..89a8200cf2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Dec 25 22:21:06 2012  Keiju Ishitsuka  <keiju@ishitsuka.com>
+
+	* lib/irb/output-method.rb: raise right exception when
+	  IRB::OutputMethod#print don't defined [Bug #6657].
+
 Tue Dec 25 22:06:33 2012  Koichi Sasada  <ko1@atdot.net>
 
 	* vm_trace.c (rb_threadptr_exec_event_hooks_and_pop_frame):
diff --git a/lib/irb/output-method.rb b/lib/irb/output-method.rb
index 541c83f24d..aae9e2294d 100644
--- a/lib/irb/output-method.rb
+++ b/lib/irb/output-method.rb
@@ -16,12 +16,14 @@ module IRB
   # IRB::Notifier. You can define your own output method to use with Irb.new,
   # or Context.new
   class OutputMethod
-    @RCS_ID='-$Id$-'
+    extend Exception2MessageMapper
+    def_exception :NotImplementedError, "Need to define `%s'"
+
 
     # Open this method to implement your own output method, raises a
     # NotImplementedError if you don't define #print in your own class.
     def print(*opts)
-      IRB.fail NotImplementedError, "print"
+      OutputMethod.Raise NotImplementedError, "print"
     end
 
     # Prints the given +opts+, with a newline delimiter.