diff --git a/ChangeLog b/ChangeLog
index 5afc319d08..538aeb2efd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Dec  6 19:02:55 2015  Kazuhiro NISHIYAMA  <zn@mbf.nifty.com>
+
+	* configure.in: add missing x.
+
 Sun Dec  6 18:25:22 2015  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* test/webrick/test_cgi.rb (TestWEBrickCGI#test_cgi): gave up the test
diff --git a/configure.in b/configure.in
index 134e024d0c..cf09ae5a38 100644
--- a/configure.in
+++ b/configure.in
@@ -1753,7 +1753,7 @@ RUBY_FUNC_ATTRIBUTE(deprecated("by "@%:@n), DEPRECATED_BY(n,x), rb_cv_func_depre
 RUBY_TYPE_ATTRIBUTE(deprecated mesg, DEPRECATED_TYPE(mesg,x), rb_cv_type_deprecated)
 RUBY_FUNC_ATTRIBUTE(noinline, NOINLINE)
 RUBY_FUNC_ATTRIBUTE(weak, WEAK, rb_cv_func_weak)
-if test "$rb_cv_func_weak" != x; then
+if test x"$rb_cv_func_weak" != x; then
    AC_DEFINE(HAVE_FUNC_WEAK)
 fi