diff --git a/ChangeLog b/ChangeLog
index ee1ee791e0..c5ee7a8d81 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Aug  8 07:47:29 2010  Tanaka Akira  <akr@fsij.org>
+
+	* lib/rbconfig/obsolete.rb: show the location which use Config.
+
 Sun Aug  8 07:29:55 2010  Tanaka Akira  <akr@fsij.org>
 
 	* ext/pathname/pathname.c (path_fnmatch): Pathname#fnmatch and
diff --git a/lib/rbconfig/obsolete.rb b/lib/rbconfig/obsolete.rb
index fcc7151ad2..eae9155af6 100644
--- a/lib/rbconfig/obsolete.rb
+++ b/lib/rbconfig/obsolete.rb
@@ -1,2 +1,5 @@
-warn "Use RbConfig instead of obsolete and deprecated Config."
+loc = caller[0]
+loc = loc[/\A.*:\d+:/] if loc
+loc = "#{loc} " if loc
+warn "#{loc}Use RbConfig instead of obsolete and deprecated Config."
 Config = RbConfig # compatibility for ruby-1.8.4 and older.