diff --git a/ChangeLog b/ChangeLog
index 57cedfa783..c1f1da233e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Aug  7 22:37:08 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
+
+	* configure.in: add -Wunused-variable to default CFLAGS.
+	  Patch by Eric Wong. [Feature #5157] [ruby-core:38798]
+
 Sun Aug  7 15:37:35 2011  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* ext/digest/sha2/sha2ossl.c: use original SHA384_Final on DragonFly.
diff --git a/configure.in b/configure.in
index 7176fda353..8140a15c0a 100644
--- a/configure.in
+++ b/configure.in
@@ -458,6 +458,7 @@ if test "$GCC:${warnflags+set}:no" = yes::no; then
     particular_werror_flags=yes
     for wflag in -Wno-unused-parameter -Wno-parentheses -Wno-long-long \
 		 -Wno-missing-field-initializers \
+		 -Wunused-variable \
 		 -Werror=pointer-arith \
 		 -Werror=write-strings \
 		 -Werror=declaration-after-statement \