diff --git a/src/common/time.cpp b/src/common/time.cpp
index 2ad2d9ad6d..c2f7f637fd 100644
--- a/src/common/time.cpp
+++ b/src/common/time.cpp
@@ -37,6 +37,10 @@
     #endif
 #endif
 
+#ifdef WX_GMTOFF_IN_TM
+    #include <atomic>
+#endif
+
 #include <time.h>
 
 wxDECL_FOR_STRICT_MINGW32(void, tzset, (void));
@@ -119,12 +123,10 @@ struct tm *wxGmtime_r(const time_t* ticks, struct tm* temp)
 int wxGetTimeZone()
 {
 #ifdef WX_GMTOFF_IN_TM
-    // set to true when the timezone is set
-    static bool s_timezoneSet = false;
-    static long gmtoffset = LONG_MAX; // invalid timezone
+    static std::atomic<int> s_gmtoffset{INT_MAX}; // invalid timezone
 
     // ensure that the timezone variable is set by calling wxLocaltime_r
-    if ( !s_timezoneSet )
+    if ( s_gmtoffset == INT_MAX )
     {
         // just call wxLocaltime_r() instead of figuring out whether this
         // system supports tzset(), _tzset() or something else
@@ -132,20 +134,21 @@ int wxGetTimeZone()
         struct tm tm;
 
         wxLocaltime_r(&t, &tm);
-        s_timezoneSet = true;
 
         // note that GMT offset is the opposite of time zone and so to return
         // consistent results in both WX_GMTOFF_IN_TM and !WX_GMTOFF_IN_TM
         // cases we have to negate it
-        gmtoffset = -tm.tm_gmtoff;
+        int gmtoffset = static_cast<int>(-tm.tm_gmtoff);
 
         // this function is supposed to return the same value whether DST is
         // enabled or not, so we need to use an additional offset if DST is on
         // as tm_gmtoff already does include it
         if ( tm.tm_isdst )
             gmtoffset += 3600;
+
+        s_gmtoffset = gmtoffset;
     }
-    return (int)gmtoffset;
+    return s_gmtoffset;
 #elif defined(__WINE__)
     struct timeb tb;
     ftime(&tb);