diff --git a/include/time.h b/include/time.h
index 52bb22abd9..e9c083646a 100644
--- a/include/time.h
+++ b/include/time.h
@@ -49,20 +49,6 @@ extern const unsigned short int __mon_yday[2][13] attribute_hidden;
 /* Defined in localtime.c.  */
 extern struct tm _tmbuf attribute_hidden;
 
-/* Defined in tzset.c.  */
-extern char *__tzstring (const char *string) attribute_hidden;
-
-extern int __use_tzfile attribute_hidden;
-
-extern void __tzfile_read (const char *file) attribute_hidden;
-extern void __tzfile_compute (__time64_t timer, int use_localtime,
-			      long int *leap_correct, int *leap_hit,
-			      struct tm *tp) attribute_hidden;
-extern void __tzset_parse_tz (const char *tz) attribute_hidden;
-extern void __tz_compute (__time64_t timer, struct tm *tm, int use_localtime)
-  __THROW attribute_hidden;
-
-
 #if __TIMESIZE == 64
 # define __itimerspec64 itimerspec
 #else
@@ -271,11 +257,6 @@ extern int __offtime (__time64_t __timer,
 
 extern char *__asctime_r (const struct tm *__tp, char *__buf)
   attribute_hidden;
-extern void __tzset (void) attribute_hidden;
-
-/* Prototype for the internal function to get information based on TZ.  */
-extern struct tm *__tz_convert (__time64_t timer, int use_localtime,
-				struct tm *tp) attribute_hidden;
 
 extern int __nanosleep (const struct timespec *__requested_time,
 			struct timespec *__remaining);
diff --git a/time/gmtime.c b/time/gmtime.c
index ad6e8eb352..9d0af33401 100644
--- a/time/gmtime.c
+++ b/time/gmtime.c
@@ -17,13 +17,17 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <time.h>
+#include <tzset.h>
 
 /* Return the `struct tm' representation of *T in UTC,
    using *TP to store the result.  */
 struct tm *
 __gmtime64_r (const __time64_t *t, struct tm *tp)
 {
-  return __tz_convert (*t, 0, tp);
+  __libc_lock_lock (__tzset_lock);
+  struct tm *result = __tz_convert (*t, 0, tp);
+  __libc_lock_unlock (__tzset_lock);
+  return result;
 }
 
 /* Provide a 32-bit variant if needed.  */
@@ -48,7 +52,7 @@ weak_alias (__gmtime_r, gmtime_r)
 struct tm *
 __gmtime64 (const __time64_t *t)
 {
-  return __tz_convert (*t, 0, &_tmbuf);
+  return __gmtime64_r (t, &_tmbuf);
 }
 
 /* Provide a 32-bit variant if needed.  */
diff --git a/time/localtime.c b/time/localtime.c
index d1967ff11b..7f865a7053 100644
--- a/time/localtime.c
+++ b/time/localtime.c
@@ -17,6 +17,7 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <time.h>
+#include <tzset.h>
 
 /* C89 says that localtime and gmtime return the same pointer.
    Although C99 and later relax this to let localtime and gmtime
@@ -30,7 +31,10 @@ struct tm _tmbuf;
 struct tm *
 __localtime64_r (const __time64_t *t, struct tm *tp)
 {
-  return __tz_convert (*t, 1, tp);
+  __libc_lock_lock (__tzset_lock);
+  struct  tm *result = __tz_convert (*t, 1, tp);
+  __libc_lock_unlock (__tzset_lock);
+  return result;
 }
 
 /* Provide a 32-bit variant if needed.  */
@@ -54,7 +58,7 @@ weak_alias (__localtime_r, localtime_r)
 struct tm *
 __localtime64 (const __time64_t *t)
 {
-  return __tz_convert (*t, 1, &_tmbuf);
+  return __localtime64_r (t, &_tmbuf);
 }
 libc_hidden_def (__localtime64)
 
diff --git a/time/mktime-internal.h b/time/mktime-internal.h
index 1da98b4373..215be914c2 100644
--- a/time/mktime-internal.h
+++ b/time/mktime-internal.h
@@ -19,6 +19,9 @@
 
 #ifndef _LIBC
 # include <time.h>
+# define __libc_lock_lock(lock) ((void) 0)
+# define __libc_lock_unlock(lock) ((void) 0)
+# define __tzset_unlocked() tzset ()
 #endif
 
 /* mktime_offset_t is a signed type wide enough to hold a UTC offset
@@ -73,6 +76,8 @@ typedef int mktime_offset_t;
 /* Subroutine of mktime.  Return the time_t representation of TP and
    normalize TP, given that a struct tm * maps to a time_t.  If
    LOCAL, the mapping is performed by localtime_r, otherwise by gmtime_r.
-   Record next guess for localtime-gmtime offset in *OFFSET.  */
+   Record next guess for localtime-gmtime offset in *OFFSET.
+
+   If _LIBC, the caller must lock __tzset_lock.  */
 extern __time64_t __mktime_internal (struct tm *tp, bool local,
                                      mktime_offset_t *offset) attribute_hidden;
diff --git a/time/mktime.c b/time/mktime.c
index 7f7d33492b..3a951b2c8c 100644
--- a/time/mktime.c
+++ b/time/mktime.c
@@ -62,6 +62,9 @@
 # define NEED_MKTIME_WORKING 0
 #endif
 
+#ifdef _LIBC
+# include <tzset.h>
+#endif
 #include "mktime-internal.h"
 
 #if !defined _LIBC && (NEED_MKTIME_WORKING || NEED_MKTIME_WINDOWS)
@@ -250,6 +253,7 @@ tm_diff (long_int year, long_int yday, int hour, int min, int sec,
 		     tp->tm_hour, tp->tm_min, tp->tm_sec);
 }
 
+#ifndef _LIBC
 /* Convert T to a struct tm value in *TM.  Use localtime64_r if LOCAL,
    otherwise gmtime64_r.  T must be in range for __time64_t.  Return
    TM if successful, NULL (setting errno) on failure.  */
@@ -262,8 +266,8 @@ convert_time (long_int t, bool local, struct tm *tm)
   else
     return __gmtime64_r (&x, tm);
 }
-/* Call it __tzconvert to sync with other parts of glibc.  */
-#define __tz_convert convert_time
+# define __tz_convert convert_time
+#endif
 
 /* Convert *T to a broken down time in *TP (as if by localtime if
    LOCAL, otherwise as if by gmtime).  If *T is out of range for
@@ -320,7 +324,9 @@ ranged_convert (bool local, long_int *t, struct tm *tp)
    If *OFFSET's guess is correct, only one reverse mapping call is
    needed.  If successful, set *TP to the canonicalized struct tm;
    otherwise leave *TP alone, return ((time_t) -1) and set errno.
-   This function is external because it is used also by timegm.c.  */
+   This function is external because it is used also by timegm.c.
+
+   If _LIBC, the caller must lock __tzset_lock.  */
 __time64_t
 __mktime_internal (struct tm *tp, bool local, mktime_offset_t *offset)
 {
@@ -548,14 +554,15 @@ __mktime_internal (struct tm *tp, bool local, mktime_offset_t *offset)
 __time64_t
 __mktime64 (struct tm *tp)
 {
-  /* POSIX.1 requires mktime to set external variables like 'tzname'
-     as though tzset had been called.  */
-  __tzset ();
-
 # if defined _LIBC || NEED_MKTIME_WORKING
+  __libc_lock_lock (__tzset_lock);
+  __tzset_unlocked ();
   static mktime_offset_t localtime_offset;
-  return __mktime_internal (tp, true, &localtime_offset);
+  __time64_t result = __mktime_internal (tp, true, &localtime_offset);
+  __libc_lock_unlock (__tzset_lock);
+  return result;
 # else
+  __tzset ();
 #  undef mktime
   return mktime (tp);
 # endif
diff --git a/time/strftime_l.c b/time/strftime_l.c
index f51d926b46..584df83d15 100644
--- a/time/strftime_l.c
+++ b/time/strftime_l.c
@@ -33,6 +33,7 @@
 # define MULTIBYTE_IS_FORMAT_SAFE 1
 # define STDC_HEADERS 1
 # include "../locale/localeinfo.h"
+# include <tzset.h>
 #endif
 
 #if defined emacs && !defined HAVE_BCOPY
diff --git a/time/timegm.c b/time/timegm.c
index 4c2615b9fa..42115a5d7f 100644
--- a/time/timegm.c
+++ b/time/timegm.c
@@ -24,13 +24,20 @@
 #include <time.h>
 #include <errno.h>
 
+#ifdef _LIBC
+# include <tzset.h>
+#endif
 #include "mktime-internal.h"
 
 __time64_t
 __timegm64 (struct tm *tmp)
 {
+  __libc_lock_lock (__tzset_lock);
+  __tzset_unlocked ();
   static mktime_offset_t gmtime_offset;
-  return __mktime_internal (tmp, false, &gmtime_offset);
+  __time64_t result = __mktime_internal (tmp, false, &gmtime_offset);
+  __libc_lock_unlock (__tzset_lock);
+  return result;
 }
 
 #if defined _LIBC && __TIMESIZE != 64
diff --git a/time/tzfile.c b/time/tzfile.c
index bca8b3f4ef..fa2be56580 100644
--- a/time/tzfile.c
+++ b/time/tzfile.c
@@ -27,6 +27,7 @@
 #include <stdint.h>
 #include <alloc_buffer.h>
 #include <set-freeres.h>
+#include <tzset.h>
 
 #include <timezone/tzfile.h>
 
diff --git a/time/tzset.c b/time/tzset.c
index 1a9a03a436..a0bf3382ba 100644
--- a/time/tzset.c
+++ b/time/tzset.c
@@ -16,13 +16,13 @@
    <https://www.gnu.org/licenses/>.  */
 
 #include <ctype.h>
-#include <libc-lock.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <time.h>
+#include <tzset.h>
 
 #include <timezone/tzfile.h>
 
@@ -37,7 +37,7 @@ weak_alias (__daylight, daylight)
 weak_alias (__timezone, timezone)
 
 /* This locks all the state variables in tzfile.c and this file.  */
-__libc_lock_define_initialized (static, tzset_lock)
+__libc_lock_define_initialized (, __tzset_lock)
 
 /* This structure contains all the information about a
    timezone given in the POSIX standard TZ envariable.  */
@@ -529,10 +529,8 @@ __tz_compute (__time64_t timer, struct tm *tm, int use_localtime)
 #undef tzset
 
 void
-__tzset (void)
+__tzset_unlocked (void)
 {
-  __libc_lock_lock (tzset_lock);
-
   tzset_internal (1);
 
   if (!__use_tzfile)
@@ -541,9 +539,16 @@ __tzset (void)
       __tzname[0] = (char *) tz_rules[0].name;
       __tzname[1] = (char *) tz_rules[1].name;
     }
+}
 
-  __libc_lock_unlock (tzset_lock);
+void
+__tzset (void)
+{
+  __libc_lock_lock (__tzset_lock);
+  __tzset_unlocked ();
+  __libc_lock_unlock (__tzset_lock);
 }
+
 weak_alias (__tzset, tzset)
 
 /* Return the `struct tm' representation of TIMER in the local timezone.
@@ -554,8 +559,6 @@ __tz_convert (__time64_t timer, int use_localtime, struct tm *tp)
   long int leap_correction;
   int leap_extra_secs;
 
-  __libc_lock_lock (tzset_lock);
-
   /* Update internal database according to current TZ setting.
      POSIX.1 8.3.7.2 says that localtime_r is not required to set tzname.
      This is a good idea since this allows at least a bit more parallelism.  */
@@ -574,8 +577,6 @@ __tz_convert (__time64_t timer, int use_localtime, struct tm *tp)
       leap_extra_secs = 0;
     }
 
-  __libc_lock_unlock (tzset_lock);
-
   if (tp)
     {
       if (! use_localtime)
diff --git a/time/tzset.h b/time/tzset.h
new file mode 100644
index 0000000000..fb7984563e
--- /dev/null
+++ b/time/tzset.h
@@ -0,0 +1,30 @@
+#ifndef _TZSET_H
+#define _TZSET_H
+
+#include <time.h>
+#include <libc-lock.h>
+
+/* Defined in tzset.c.  */
+extern char *__tzstring (const char *string) attribute_hidden;
+
+extern int __use_tzfile attribute_hidden;
+
+extern void __tzfile_read (const char *file) attribute_hidden;
+extern void __tzfile_compute (__time64_t timer, int use_localtime,
+			      long int *leap_correct, int *leap_hit,
+			      struct tm *tp) attribute_hidden;
+extern void __tzset_parse_tz (const char *tz) attribute_hidden;
+extern void __tz_compute (__time64_t timer, struct tm *tm, int use_localtime)
+  __THROW attribute_hidden;
+
+__libc_lock_define (extern, __tzset_lock attribute_hidden);
+
+extern void __tzset (void) attribute_hidden;
+extern void __tzset_unlocked (void) attribute_hidden;
+
+/* Prototype for the internal function to get information based on TZ.
+   Caller needs to lock __tzset_lock.  */
+extern struct tm *__tz_convert (__time64_t timer, int use_localtime,
+				struct tm *tp) attribute_hidden;
+
+#endif /* _TZSET_H */