diff --git a/ChangeLog b/ChangeLog
index fdb87af617..274e60aa75 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Nov  8 11:32:11 2012  Akinori MUSHA  <knu@iDaemons.org>
+
+	* configure.in (--with-opt-dir): Avoid nesting of double quotes
+	  inside backquotes, since some traditional shells like PD KSH
+	  (which OpenBSD's /bin/sh bases on) fails to parse them.
+
 Thu Nov  8 09:34:00 2012  Kenta Murata  <mrkn@cookpad.com>
 
 	* numeric.c: Add description of that the results of the comparing
diff --git a/configure.in b/configure.in
index a3d8a6795c..252525dce9 100644
--- a/configure.in
+++ b/configure.in
@@ -2304,7 +2304,8 @@ AC_ARG_WITH(opt-dir,
 	AS_HELP_STRING([--with-opt-dir=DIR-LIST],
 		       [add optional headers and libraries directories separated by $PATH_SEPARATOR]),
 	[
-		CPPFLAGS="$CPPFLAGS `echo \"$PATH_SEPARATOR$withval\" | sed \"s|$PATH_SEPARATOR\([[^$PATH_SEPARATOR]*]\)| -I\1/include|g;s/^ //\"`"
+		val=`echo "$PATH_SEPARATOR$withval" | sed "s|$PATH_SEPARATOR\([[^$PATH_SEPARATOR]*]\)| -I\1/include|g;s/^ //"`
+		CPPFLAGS="$CPPFLAGS $val"
 		set -x
 		val=`IFS="$PATH_SEPARATOR"
 		    for dir in $withval; do