diff --git a/conf/Makefile.nps b/conf/Makefile.nps
index 2fcebaa429..2c6fc6eabf 100644
--- a/conf/Makefile.nps
+++ b/conf/Makefile.nps
@@ -50,7 +50,7 @@ CXXFLAGS += -O$(OPT)
 CXXFLAGS += $(DEBUG_FLAGS)
 CXXFLAGS += $(shell pkg-config --cflags-only-I ivy-glib)
 
-LDFLAGS	+= $($(TARGET).LDFLAGS) -pthread
+LDFLAGS	+= $($(TARGET).LDFLAGS)
 LDFLAGS += $(BOARD_LDFLAGS)
 
 # x86/64 and armv7 allow unaligned access
diff --git a/conf/firmwares/subsystems/shared/nps.makefile b/conf/firmwares/subsystems/shared/nps.makefile
index af06073b9a..6a3179b22f 100644
--- a/conf/firmwares/subsystems/shared/nps.makefile
+++ b/conf/firmwares/subsystems/shared/nps.makefile
@@ -17,7 +17,14 @@ nps.ARCHDIR = sim
 nps.MAKEFILE = nps
 
 nps.CFLAGS  += -DSITL -DUSE_NPS
-nps.LDFLAGS += -lm -livy $(shell pcre-config --libs) -lgsl -lgslcblas -lrt
+nps.LDFLAGS += -lm -livy $(shell pcre-config --libs) -lgsl -lgslcblas
+
+# detect system arch and include rt and pthread library only on linux
+UNAME_S := $(shell uname -s)
+ifeq ($(UNAME_S),Linux)
+  nps.LDFLAGS += -lrt -pthread
+endif
+
 nps.CFLAGS  += -I$(SRC_FIRMWARE) -I$(SRC_BOARD) -I$(PAPARAZZI_SRC)/sw/simulator -I$(PAPARAZZI_SRC)/sw/simulator/nps -I$(PAPARAZZI_HOME)/conf/simulator/nps
 
 # sdl needed for joystick input
@@ -52,10 +59,8 @@ nps.srcs +=                                      \
        $(NPSDIR)/nps_main_common.c
 
 ifeq ($(USE_HITL),1)
-$(info USE_HITL defined)
 include $(CFG_SHARED)/nps_hitl.makefile
 else
-$(info USE_HITL undefined)
 include $(CFG_SHARED)/nps_sitl.makefile
 endif
 
diff --git a/sw/simulator/nps/nps_main.h b/sw/simulator/nps/nps_main.h
index c6c9c2f4d4..56dbeea00b 100644
--- a/sw/simulator/nps/nps_main.h
+++ b/sw/simulator/nps/nps_main.h
@@ -9,6 +9,14 @@
 #include "nps_sensors.h"
 #include "nps_autopilot.h"
 
+#ifdef __MACH__ // OS X does not have clock_gettime, use clock_get_time
+#include <mach/clock.h>
+#include <mach/mach.h>
+void clock_get_current_time(struct timespec *ts);
+#else // Linux
+#define clock_get_current_time(_x) clock_gettime(CLOCK_REALTIME, _x)
+#endif // #ifdef __MACH__
+
 #define SIM_DT     (1./SYS_TIME_FREQUENCY)
 #define DISPLAY_DT (1./30.)
 #define HOST_TIMEOUT_MS 40
diff --git a/sw/simulator/nps/nps_main_common.c b/sw/simulator/nps/nps_main_common.c
index bf470eac52..3c2d401ba8 100644
--- a/sw/simulator/nps/nps_main_common.c
+++ b/sw/simulator/nps/nps_main_common.c
@@ -30,6 +30,22 @@
 
 #include "nps_ivy.h"
 
+#ifdef __MACH__
+pthread_mutex_t clock_mutex; // mutex for clock
+void clock_get_current_time(struct timespec *ts)
+{
+  pthread_mutex_lock(&clock_mutex);
+  clock_serv_t cclock;
+  mach_timespec_t mts;
+  host_get_clock_service(mach_host_self(), CALENDAR_CLOCK, &cclock);
+  clock_get_time(cclock, &mts);
+  mach_port_deallocate(mach_task_self(), cclock);
+  ts->tv_sec = mts.tv_sec;
+  ts->tv_nsec = mts.tv_nsec;
+  pthread_mutex_unlock(&clock_mutex);
+}
+#endif
+
 void tstp_hdl(int n __attribute__((unused)))
 {
   if (pauseSignal) {
@@ -239,7 +255,7 @@ void *nps_flight_gear_loop(void *data __attribute__((unused)))
   nps_flightgear_init(nps_main.fg_host, nps_main.fg_port, nps_main.fg_port_in, nps_main.fg_time_offset);
 
   while (TRUE) {
-    clock_gettime(CLOCK_REALTIME, &requestStart);
+    clock_get_current_time(&requestStart);
 
     pthread_mutex_lock(&fdm_mutex);
     if (nps_main.fg_host) {
@@ -251,7 +267,7 @@ void *nps_flight_gear_loop(void *data __attribute__((unused)))
     }
     pthread_mutex_unlock(&fdm_mutex);
 
-    clock_gettime(CLOCK_REALTIME, &requestEnd);
+    clock_get_current_time(&requestEnd);
 
     // Calculate time it took
     task_ns = (requestEnd.tv_sec - requestStart.tv_sec) * 1000000000L + (requestEnd.tv_nsec - requestStart.tv_nsec);
@@ -287,7 +303,7 @@ void *nps_main_display(void *data __attribute__((unused)))
   nps_ivy_init(nps_main.ivy_bus);
 
   while (TRUE) {
-    clock_gettime(CLOCK_REALTIME, &requestStart);
+    clock_get_current_time(&requestStart);
 
     pthread_mutex_lock(&fdm_mutex);
     memcpy(&fdm_ivy, &fdm, sizeof(fdm));
@@ -296,7 +312,7 @@ void *nps_main_display(void *data __attribute__((unused)))
 
     nps_ivy_display(&fdm_ivy, &sensors_ivy);
 
-    clock_gettime(CLOCK_REALTIME, &requestEnd);
+    clock_get_current_time(&requestEnd);
 
     // Calculate time it took
     task_ns = (requestEnd.tv_sec - requestStart.tv_sec) * 1000000000L + (requestEnd.tv_nsec - requestStart.tv_nsec);
diff --git a/sw/simulator/nps/nps_main_hitl.c b/sw/simulator/nps/nps_main_hitl.c
index 6177629f68..6f40547960 100644
--- a/sw/simulator/nps/nps_main_hitl.c
+++ b/sw/simulator/nps/nps_main_hitl.c
@@ -138,7 +138,7 @@ void *nps_ins_data_loop(void *data __attribute__((unused)))
     pthread_mutex_lock(&fdm_mutex);
 
     // start timing
-    clock_gettime(CLOCK_REALTIME, &requestStart);
+    clock_get_current_time(&requestStart);
 
     // make a copy of fdm struct to speed things up
     memcpy(&fdm_ins, &fdm, sizeof(fdm));
@@ -159,7 +159,7 @@ void *nps_ins_data_loop(void *data __attribute__((unused)))
       printf("INS THREAD: Warning - sent only %u bytes to the autopilot, instead of expected %u\n", wlen, idx);
     }
 
-    clock_gettime(CLOCK_REALTIME, &requestEnd);
+    clock_get_current_time(&requestEnd);
 
     // Calculate time it took
     task_ns = (requestEnd.tv_sec - requestStart.tv_sec) * 1000000000L + (requestEnd.tv_nsec - requestStart.tv_nsec);
@@ -285,19 +285,19 @@ void *nps_main_loop(void *data __attribute__((unused)))
   // fdm.time - simulation time
   struct timespec startTime;
   struct timespec realTime;
-  clock_gettime(CLOCK_REALTIME, &startTime);
+  clock_get_current_time(&startTime);
   double start_secs = ntime_to_double(&startTime);
   double real_secs = 0;
   double real_time = 0;
   static int guard;
 
   while (TRUE) {
-    clock_gettime(CLOCK_REALTIME, &requestStart);
+    clock_get_current_time(&requestStart);
 
     pthread_mutex_lock(&fdm_mutex);
 
     // check the current simulation time
-    clock_gettime(CLOCK_REALTIME, &realTime);
+    clock_get_current_time(&realTime);
     real_secs = ntime_to_double(&realTime);
     real_time = real_secs - start_secs; // real time elapsed
 
@@ -312,7 +312,7 @@ void *nps_main_loop(void *data __attribute__((unused)))
     }
     pthread_mutex_unlock(&fdm_mutex);
 
-    clock_gettime(CLOCK_REALTIME, &requestEnd);
+    clock_get_current_time(&requestEnd);
 
     // Calculate time it took
     task_ns = (requestEnd.tv_sec - requestStart.tv_sec) * 1000000000L + (requestEnd.tv_nsec - requestStart.tv_nsec);
diff --git a/sw/simulator/nps/nps_main_sitl.c b/sw/simulator/nps/nps_main_sitl.c
index bf2b03fb84..ebf28b7058 100644
--- a/sw/simulator/nps/nps_main_sitl.c
+++ b/sw/simulator/nps/nps_main_sitl.c
@@ -127,7 +127,7 @@ void *nps_main_loop(void *data __attribute__((unused)))
       pauseSignal = 0;
     }
 
-    clock_gettime(CLOCK_REALTIME, &requestStart); // init measurement (after the pause signal)
+    clock_get_current_time(&requestStart); // init measurement (after the pause signal)
 
     gettimeofday(&tv_now, NULL);
     host_time_now = time_to_double(&tv_now);
@@ -163,7 +163,7 @@ void *nps_main_loop(void *data __attribute__((unused)))
     printf("%f,%f\n", nps_main.sim_time, nps_main.display_time);
 #endif
 
-    clock_gettime(CLOCK_REALTIME, &requestEnd); // end measurement
+    clock_get_current_time(&requestEnd); // end measurement
 
     // Calculate time it took
     task_ns = (requestEnd.tv_sec - requestStart.tv_sec) * 1000000000L + (requestEnd.tv_nsec - requestStart.tv_nsec);