diff --git a/libraries/SITL/SIM_GPS_MSP.cpp b/libraries/SITL/SIM_GPS_MSP.cpp
index 125f1b8de2..2bf9db476f 100644
--- a/libraries/SITL/SIM_GPS_MSP.cpp
+++ b/libraries/SITL/SIM_GPS_MSP.cpp
@@ -56,7 +56,8 @@ void GPS_MSP::publish(const GPS_Data *d)
     auto t = gps_time();
     struct timeval tv;
     simulation_timeval(&tv);
-    auto *tm = gmtime(&tv.tv_sec);
+    struct tm tvd {};
+    auto *tm = gmtime_r(&tv.tv_sec, &tvd);
 
     msp_gps.gps_week = t.week;
     msp_gps.ms_tow = t.ms;
diff --git a/libraries/SITL/SIM_GPS_NMEA.cpp b/libraries/SITL/SIM_GPS_NMEA.cpp
index 161f0ef0f0..c4b16b89da 100644
--- a/libraries/SITL/SIM_GPS_NMEA.cpp
+++ b/libraries/SITL/SIM_GPS_NMEA.cpp
@@ -45,7 +45,8 @@ void GPS_NMEA::publish(const GPS_Data *d)
 
     simulation_timeval(&tv);
 
-    tm = gmtime(&tv.tv_sec);
+    struct tm tvd {};
+    tm = gmtime_r(&tv.tv_sec, &tvd);
 
     // format time string
     hal.util->snprintf(tstring, sizeof(tstring), "%02u%02u%06.3f", tm->tm_hour, tm->tm_min, tm->tm_sec + tv.tv_usec*1.0e-6);