--- /usr/src/lib/libc/stdtime/localtime.c	Wed Mar  8 13:46:25 2000
+++ /usr/src/lib/libc/stdtime/localtime.c	Tue Dec 19 14:38:00 2000
@@ -170,6 +170,7 @@
 
 static char		lcl_TZname[TZ_STRLEN_MAX + 1];
 static int		lcl_is_set;
+int			lcl_tz_is_set_by_Zlo;
 static int		gmt_is_set;
 #ifdef	_THREAD_SAFE
 static struct pthread_mutex	_lcl_mutexd = PTHREAD_MUTEX_STATIC_INITIALIZER;
@@ -989,6 +990,11 @@
 		return;
 	}
 
+	/*  N.B. when TZ has changed in the environment, you'll have to call
+	 *  tzset() from your program yourself. Zlo.
+	 */
+	lcl_tz_is_set_by_Zlo = 1;
+
 	if (lcl_is_set > 0  &&  strcmp(lcl_TZname, name) == 0)
 		return;
 	lcl_is_set = (strlen(name) < sizeof(lcl_TZname));
@@ -1126,12 +1132,15 @@
 		pthread_setspecific(localtime_key, p_tm);
 	}
 	pthread_mutex_lock(&lcl_mutex);
-	tzset();
+	if (!lcl_tz_is_set_by_Zlo)
+		tzset();
 	localsub(timep, 0L, p_tm);
 	pthread_mutex_unlock(&lcl_mutex);
 	return p_tm;
 #else
-	tzset();
+	if (!lcl_tz_is_set_by_Zlo)
+		tzset();
+
 	localsub(timep, 0L, &tm);
 	return &tm;
 #endif
@@ -1639,7 +1648,9 @@
 #ifdef	_THREAD_SAFE
 	pthread_mutex_lock(&lcl_mutex);
 #endif
-	tzset();
+	if (!lcl_tz_is_set_by_Zlo)
+		tzset();
+
 	mktime_return_value = time1(tmp, localsub, 0L);
 #ifdef	_THREAD_SAFE
 	pthread_mutex_unlock(&lcl_mutex);
@@ -1732,7 +1743,8 @@
 time2posix(t)
 time_t	t;
 {
-	tzset();
+	if (!lcl_tz_is_set_by_Zlo)
+		tzset();
 	return t - leapcorr(&t);
 }
 
@@ -1743,7 +1755,8 @@
 	time_t	x;
 	time_t	y;
 
-	tzset();
+	if (!lcl_tz_is_set_by_Zlo)
+		tzset();
 	/*
 	** For a positive leap second hit, the result
 	** is not unique.  For a negative leap second
--- /usr/src/lib/libc/stdtime/strftime.c	Thu Oct 26 16:25:02 2000
+++ /usr/src/lib/libc/stdtime/strftime.c	Tue Dec 19 14:38:00 2000
@@ -60,7 +60,9 @@
 {
 	char *p;
 
-	tzset();
+	if (!lcl_tz_is_set_by_Zlo)
+		tzset();
+
 	p = _fmt(((format == NULL) ? "%c" : format), t, s, s + maxsize);
 	if (p == s + maxsize)
 		return 0;
--- /usr/src/lib/libc/stdtime/tzfile.h	Thu Jan 21 18:22:59 1999
+++ /usr/src/lib/libc/stdtime/tzfile.h	Tue Dec 19 14:38:00 2000
@@ -15,6 +15,8 @@
 ** Thank you!
 */
 
+extern int	lcl_tz_is_set_by_Zlo;
+
 /*
 ** ID
 */