diff --git a/ChangeLog b/ChangeLog
index 3209353025..f7a8f9bccc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Mon Jun 12 23:41:54 2000  WATANABE Hirofumi  <eban@os.rim.or.jp>
+
+	* configure.in (daylight): avoid GCC optimization.
+
+Mon Jun 12 19:02:27 2000  WATANABE Hirofumi  <eban@os.rim.or.jp>
+
+	* configure.in: cygwin has strange timezone.
+
+	* time.c (time_zone): use tzname and daylight.
+
 Sat Jun 10 23:10:32 2000  Yukihiro Matsumoto  <matz@netlab.co.jp>
 
 	* io.c (rb_io_seek): whence is optional, default is SEEK_SET.
diff --git a/configure.in b/configure.in
index 242ce7f172..353bddbf61 100644
--- a/configure.in
+++ b/configure.in
@@ -157,7 +157,7 @@ openstep*)	;;
 rhapsody*)	;;
 human*)		ac_cv_func_getpgrp_void=yes;;
 beos*)		;;
-cygwin*)	;;
+cygwin*)	rb_cv_have_daylight=no;;
 mingw*)		LIBS="-lwsock32 -lmsvcrt $LIBS"
 		ac_cv_header_a_out_h=no
 		ac_cv_header_pwd_h=no
@@ -211,7 +211,7 @@ AC_CHECK_FUNCS(fmod killpg drand48 random wait4 waitpid syscall getcwd\
 AC_STRUCT_TIMEZONE
 AC_CACHE_CHECK(for external int daylight, rb_cv_have_daylight,
   [AC_TRY_LINK([],
-  	[extern int daylight; int i = daylight;],
+  	[extern int daylight; daylight++;],
 	rb_cv_have_daylight=yes,
 	rb_cv_have_daylight=no)])
 if test "$rb_cv_have_daylight" = yes; then
diff --git a/time.c b/time.c
index c26ec02e4e..c47413525c 100644
--- a/time.c
+++ b/time.c
@@ -272,6 +272,11 @@ static VALUE time_gmtime _((VALUE));
 static VALUE time_localtime _((VALUE));
 static VALUE time_get_tm _((VALUE, int));
 
+#if defined(HAVE_DAYLIGHT) && !defined __MINGW32__
+extern int daylight;
+extern long timezone;
+#endif
+
 static time_t
 make_time_t(tptr, utc_or_local)
     struct tm *tptr;
@@ -313,9 +318,6 @@ make_time_t(tptr, utc_or_local)
 
     if (!utc_or_local) {	/* localtime zone adjust */
 #if defined(HAVE_DAYLIGHT)
-	extern int daylight;
-	extern long timezone;
-
 	localtime(&guess);
 	guess += timezone + daylight;
 #else
@@ -807,8 +809,8 @@ time_zone(time)
 	time_get_tm(time, tobj->gmt);
     }
 
-#ifdef HAVE_TZNAME
-    return rb_str_new2(tobj->tm.tm_zone);
+#if defined HAVE_TZNAME && defined HAVE_DAYLIGHT
+    return rb_str_new2(tzname[daylight && tobj->tm.tm_isdst]);
 #else
     len = strftime(buf, 64, "%Z", &tobj->tm);
     return rb_str_new(buf, len);