diff --git a/src/auto/configure b/src/auto/configure
index c326abf..8dcad0b 100755
--- a/src/auto/configure
+++ b/src/auto/configure
@@ -12569,7 +12569,7 @@
 	memset mkdtemp nanosleep opendir putenv qsort readlink select setenv \
 	getpgid setpgid setsid sigaltstack sigstack sigset sigsetjmp sigaction \
 	sigprocmask sigvec strcasecmp strerror strftime stricmp strncasecmp \
-	strnicmp strpbrk strtol tgetent towlower towupper iswupper \
+	strnicmp strpbrk strtol tgetent towlower towupper iswupper tzset \
 	usleep utime utimes mblen ftruncate unsetenv posix_openpt
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
diff --git a/src/config.h.in b/src/config.h.in
index c1ced6f..f9ae0bb 100644
--- a/src/config.h.in
+++ b/src/config.h.in
@@ -217,6 +217,7 @@
 #undef HAVE_TOWLOWER
 #undef HAVE_TOWUPPER
 #undef HAVE_ISWUPPER
+#undef HAVE_TZSET
 #undef HAVE_UNSETENV
 #undef HAVE_USLEEP
 #undef HAVE_UTIME
diff --git a/src/configure.ac b/src/configure.ac
index dbf4f42..f7a71d0 100644
--- a/src/configure.ac
+++ b/src/configure.ac
@@ -3742,7 +3742,7 @@
 	memset mkdtemp nanosleep opendir putenv qsort readlink select setenv \
 	getpgid setpgid setsid sigaltstack sigstack sigset sigsetjmp sigaction \
 	sigprocmask sigvec strcasecmp strerror strftime stricmp strncasecmp \
-	strnicmp strpbrk strtol tgetent towlower towupper iswupper \
+	strnicmp strpbrk strtol tgetent towlower towupper iswupper tzset \
 	usleep utime utimes mblen ftruncate unsetenv posix_openpt)
 AC_FUNC_SELECT_ARGTYPES
 AC_FUNC_FSEEKO
diff --git a/src/evalfunc.c b/src/evalfunc.c
index 66612e8..5c9400e 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -13188,9 +13188,7 @@
 f_strftime(typval_T *argvars, typval_T *rettv)
 {
     char_u	result_buf[256];
-# ifdef HAVE_LOCALTIME_R
     struct tm	tmval;
-# endif
     struct tm	*curtime;
     time_t	seconds;
     char_u	*p;
@@ -13202,11 +13200,7 @@
 	seconds = time(NULL);
     else
 	seconds = (time_t)tv_get_number(&argvars[1]);
-# ifdef HAVE_LOCALTIME_R
-    curtime = localtime_r(&seconds, &tmval);
-# else
-    curtime = localtime(&seconds);
-# endif
+    curtime = vim_localtime(&seconds, &tmval);
     /* MSVC returns NULL for an invalid value of seconds. */
     if (curtime == NULL)
 	rettv->vval.v_string = vim_strsave((char_u *)_("(Invalid)"));
diff --git a/src/memline.c b/src/memline.c
index e7ae6df..0e3bdb8 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -2082,6 +2082,48 @@
 #endif
 
 /*
+ * Cache of the current timezone name as retrieved from TZ, or an empty string
+ * where unset, up to 64 octets long including trailing null byte.
+ */
+#if defined(HAVE_LOCALTIME_R) && defined(HAVE_TZSET)
+static char	tz_cache[64];
+#endif
+
+/*
+ * Call either localtime(3) or localtime_r(3) from POSIX libc time.h, with the
+ * latter version preferred for reentrancy.
+ *
+ * If we use localtime_r(3) and we have tzset(3) available, check to see if the
+ * environment variable TZ has changed since the last run, and call tzset(3) to
+ * update the global timezone variables if it has.  This is because the POSIX
+ * standard doesn't require localtime_r(3) implementations to do that as it
+ * does with localtime(3), and we don't want to call tzset(3) every time.
+ */
+    struct tm *
+vim_localtime(
+    const time_t	*timep,		// timestamp for local representation
+    struct tm		*result)	// pointer to caller return buffer
+{
+#ifdef HAVE_LOCALTIME_R
+# ifdef HAVE_TZSET
+    char		*tz;		// pointer for TZ environment var
+
+    tz = (char *)mch_getenv((char_u *)"TZ");
+    if (tz == NULL)
+	tz = "";
+    if (STRNCMP(tz_cache, tz, sizeof(tz_cache) - 1) != 0)
+    {
+	tzset();
+	vim_strncpy((char_u *)tz_cache, (char_u *)tz, sizeof(tz_cache) - 1);
+    }
+# endif	// HAVE_TZSET
+    return localtime_r(timep, result);
+#else
+    return localtime(timep);
+#endif	// HAVE_LOCALTIME_R
+}
+
+/*
  * Replacement for ctime(), which is not safe to use.
  * Requires strftime(), otherwise returns "(unknown)".
  * If "thetime" is invalid returns "(invalid)".  Never returns NULL.
@@ -2093,16 +2135,10 @@
 {
     static char buf[50];
 #ifdef HAVE_STRFTIME
-# ifdef HAVE_LOCALTIME_R
     struct tm	tmval;
-# endif
     struct tm	*curtime;
 
-# ifdef HAVE_LOCALTIME_R
-    curtime = localtime_r(&thetime, &tmval);
-# else
-    curtime = localtime(&thetime);
-# endif
+    curtime = vim_localtime(&thetime, &tmval);
     /* MSVC returns NULL for an invalid value of seconds. */
     if (curtime == NULL)
 	vim_strncpy((char_u *)buf, (char_u *)_("(Invalid)"), sizeof(buf) - 1);
diff --git a/src/proto/memline.pro b/src/proto/memline.pro
index 3199ba9..663930d 100644
--- a/src/proto/memline.pro
+++ b/src/proto/memline.pro
@@ -13,6 +13,7 @@
 int recover_names(char_u *fname, int list, int nr, char_u **fname_out);
 char_u *make_percent_swname(char_u *dir, char_u *name);
 void get_b0_dict(char_u *fname, dict_T *d);
+struct tm *vim_localtime(const time_t *timep, struct tm *result);
 char *get_ctime(time_t thetime, int add_newline);
 void ml_sync_all(int check_file, int check_char);
 void ml_preserve(buf_T *buf, int message);
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index a2e4da6..f71717f 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -187,6 +187,30 @@
 
   call assert_fails('call strftime([])', 'E730:')
   call assert_fails('call strftime("%Y", [])', 'E745:')
+
+  " Check that the time changes after we change the timezone
+  " Save previous timezone value, if any
+  if exists('$TZ')
+    let tz = $TZ
+  endif
+
+  " Force EST and then UTC, save the current hour (24-hour clock) for each
+  let $TZ = 'EST' | let est = strftime('%H')
+  let $TZ = 'UTC' | let utc = strftime('%H')
+
+  " Those hours should be two bytes long, and should not be the same; if they
+  " are, a tzset(3) call may have failed somewhere
+  call assert_equal(strlen(est), 2)
+  call assert_equal(strlen(utc), 2)
+  call assert_notequal(est, utc)
+
+  " If we cached a timezone value, put it back, otherwise clear it
+  if exists('tz')
+    let $TZ = tz
+  else
+    unlet $TZ
+  endif
+
 endfunc
 
 func Test_resolve_unix()
diff --git a/src/undo.c b/src/undo.c
index dd46670..4a4a33c 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -3111,18 +3111,12 @@
 u_add_time(char_u *buf, size_t buflen, time_t tt)
 {
 #ifdef HAVE_STRFTIME
-# ifdef HAVE_LOCALTIME_R
     struct tm	tmval;
-# endif
     struct tm	*curtime;
 
     if (vim_time() - tt >= 100)
     {
-# ifdef HAVE_LOCALTIME_R
-	curtime = localtime_r(&tt, &tmval);
-# else
-	curtime = localtime(&tt);
-# endif
+	curtime = vim_localtime(&tt, &tmval);
 	if (vim_time() - tt < (60L * 60L * 12L))
 	    /* within 12 hours */
 	    (void)strftime((char *)buf, buflen, "%H:%M:%S", curtime);
diff --git a/src/version.c b/src/version.c
index 86ccdf4..677279b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1567,
+/**/
     1566,
 /**/
     1565,