diff --git a/ChangeLog b/ChangeLog
index 618d6997e8..5fc8702e5b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Jun 14 10:16:07 2012  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* configure.in: revert r36071 and add NetBSD to blacklist of -ansi.
+
 Thu Jun 14 07:59:12 2012  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* thread_pthread.c (get_stack): Linux is the only OS which includes
diff --git a/configure.in b/configure.in
index c594b2d51a..de2207360a 100644
--- a/configure.in
+++ b/configure.in
@@ -617,14 +617,14 @@ if test "$GCC" = yes; then
       # comments.   We  bypass  ANSI   C  mode  for  them.   Otherwise
       # extension libs cannot include those headers.
     ],
-    [cygwin*|darwin*], [
+    [cygwin*|darwin*|netbsd*], [
       # need lgamma_r(), finite()
     ],
     [
       # ANSI (no XCFLAGS because this is C only)
-      RUBY_TRY_CFLAGS(-ansi -std=iso9899:199409 -fbuiltin, [
-        RUBY_APPEND_OPTION(warnflags, -ansi -std=iso9899:199409 -fbuiltin)
-        RUBY_APPEND_OPTION(rb_cv_warnflags, -ansi -std=iso9899:199409 -fbuiltin)
+      RUBY_TRY_CFLAGS(-ansi -std=iso9899:199409, [
+        RUBY_APPEND_OPTION(warnflags, -ansi -std=iso9899:199409)
+        RUBY_APPEND_OPTION(rb_cv_warnflags, -ansi -std=iso9899:199409)
       ])
     ])