diff --git a/ChangeLog b/ChangeLog
index 82d6bbd2e7..cc6d491989 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Aug 26 09:27:10 2014  SHIBATA Hiroshi  <shibata.hiroshi@gmail.com>
+
+	* lib/mathn.rb: mathn library is deprecated on ruby 2.2.
+	  [Feature #10169][ruby-core:64553]
+
 Tue Aug 26 09:25:03 2014  SHIBATA Hiroshi  <shibata.hiroshi@gmail.com>
 
 	* lib/mathn.rb: removed commented-out code.
diff --git a/NEWS b/NEWS
index 08c6ddc887..2754d8cc08 100644
--- a/NEWS
+++ b/NEWS
@@ -121,6 +121,9 @@ with all sufficient information, see the ChangeLog file.
 
 === Stdlib compatibility issues (excluding feature bug fixes)
 
+* lib/mathn.rb
+  * Show deprecated warning [Feature #10169]
+
 * ext/date/lib/date/format.rb
   * Removed because it's empty file.
 
diff --git a/lib/mathn.rb b/lib/mathn.rb
index b18a0edb25..004f41748e 100644
--- a/lib/mathn.rb
+++ b/lib/mathn.rb
@@ -38,6 +38,8 @@
 # class Numeric follows to make this documentation findable in a reasonable
 # location
 
+warn('lib/mathn.rb is deprecated') if $VERBOSE
+
 class Numeric; end
 
 require "cmath.rb"