diff --git a/simulator/data_recorder.c b/simulator/data_recorder.c
index 0daeafd..41475f8 100644
--- a/simulator/data_recorder.c
+++ b/simulator/data_recorder.c
@@ -18,7 +18,7 @@ static int32_t values[MAX_PINS];       ///< Pin and value states
 static int pin_count;                  ///< Number of pins we emit
 static void emit_log_data(void);
 
-static void recorder_close(int code, void*x ) {
+static void recorder_close(void) {
   if (!file) return;
   // force last line to emit
   emit_log_data();
@@ -42,7 +42,7 @@ void recorder_init(const char* filename) {
   fprintf(file, "#\n");
 
   fflush(file);
-  on_exit(recorder_close, NULL);
+  atexit((void*)recorder_close);
 }
 
 void add_trace_var(const char* name, int pin) {
diff --git a/simulator/timer_ext.c b/simulator/timer_ext.c
index 25858b3..f7f05e1 100644
--- a/simulator/timer_ext.c
+++ b/simulator/timer_ext.c
@@ -5,7 +5,13 @@
 #include "dda_queue.h"
 #include "timer.h"
 #include "simulator.h"
-#include <time.h>
+#ifdef __MACH__
+  #include <mach/mach_time.h>
+  #define CLOCK_REALTIME 0
+  #define CLOCK_MONOTONIC 0
+#else
+  #include <time.h>
+#endif
 #include <stdio.h> // printf
 #include <unistd.h> // usleep
 
@@ -28,6 +34,21 @@ static volatile uint8_t timer_reason;  // Who scheduled this timer
 static uint64_t ticks;
 static uint32_t warpTarget;
 
+#ifdef __MACH__
+int clock_gettime(int clk_id, struct timespec *t) {
+  mach_timebase_info_data_t timebase;
+  mach_timebase_info(&timebase);
+  uint64_t time;
+
+  time = mach_absolute_time();
+  double nseconds = ((double)time * (double)timebase.numer)/((double)timebase.denom);
+  double seconds = ((double)time * (double)timebase.numer)/((double)timebase.denom * 1e9);
+  t->tv_sec = seconds;
+  t->tv_nsec = nseconds;
+  return 0;
+}
+#endif
+
 static uint64_t now_ns(void) {
   struct timespec tv;