diff --git a/c_src/duration.h b/c_src/duration.h
index 587a694..fbc97cb 100644
--- a/c_src/duration.h
+++ b/c_src/duration.h
@@ -13,6 +13,28 @@
 #include <time.h>
 #include <sys/timeb.h>
 
+#ifdef __MACH__
+#include <mach/clock.h>
+#include <mach/mach.h>
+#endif
+
+
+void current_utc_time(struct timespec *ts)
+{
+#ifdef __MACH__ // OS X does not have clock_gettime, use clock_get_time
+    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;
+#else
+    clock_gettime(CLOCK_REALTIME, ts);
+#endif
+
+}
+
 typedef enum { ns = 0, mcs, ms, s } time_scale;
 struct scale_time {
      const char *abbreviation;
@@ -28,9 +50,9 @@ static const struct scale_time scale[] = {
 static uint64_t ts(time_scale unit)
 {
     struct timespec ts;
-    clock_gettime(CLOCK_REALTIME, &ts);
+    current_utc_time(&ts);
     return (((uint64_t)ts.tv_sec * scale[unit].mul) +
-            ((uint64_t)ts.tv_nsec / scale[unit].div));
+	    ((uint64_t)ts.tv_nsec / scale[unit].div));
 }
 
 #if defined(__i386__) || defined(__x86_64__)
@@ -45,11 +67,9 @@ static inline uint64_t cpu_clock_ticks()
 {
      uint32_t lo, hi;
      __asm__ __volatile__ (
-	 "; Flush the pipeline"
-	 "XORL %%eax, %%eax\n"
+	 "XORL %%eax, %%eax\n" /* Flush the pipeline */
 	 "CPUID\n"
-	 "; Get RDTSC counter in edx:eax"
-	 "RDTSC\n"
+	 "RDTSC\n"             /* Get RDTSC counter in edx:eax */
 	 : "=a" (lo), "=d" (hi)
 	 :
 	 : "%ebx", "%ecx" );
@@ -90,14 +110,14 @@ static inline uint64_t elapsed(duration_t *d)
 
 #define ELAPSED_DURING(result, resolution, block)       \
      do {                                               \
-          DURATION(__x, resolution);                    \
-          do block while(0);                            \
-          *result = elapsed(&__x);                      \
+	  DURATION(__x, resolution);                    \
+	  do block while(0);                            \
+	  *result = elapsed(&__x);                      \
      } while(0);
 
 #define CYCLES_DURING(result, block)                    \
      do {                                               \
-         uint64_t __begin = cpu_clock_ticks();          \
-         do block while(0);                             \
-         *result = cpu_clock_ticks() - __begin;         \
+	 uint64_t __begin = cpu_clock_ticks();          \
+	 do block while(0);                             \
+	 *result = cpu_clock_ticks() - __begin;         \
      } while(0);
diff --git a/c_src/stats.h b/c_src/stats.h
index 2f465be..f44319b 100644
--- a/c_src/stats.h
+++ b/c_src/stats.h
@@ -152,7 +152,7 @@ static unsigned int __log2_64(uint64_t x) {
              fprintf(stderr, "     ns        μs        ms        s         ks\n"); \
              fprintf(stderr, "min: ");                                  \
              if (s->min < 1000)                                         \
-                 fprintf(stderr, "%lu (ns)", s->min);                   \
+                 fprintf(stderr, "%llu (ns)", s->min);                  \
              else if (s->min < 1000000)                                 \
                  fprintf(stderr, "%.2f (μs)", s->min / 1000.0);         \
              else if (s->min < 1000000000)                              \
@@ -161,7 +161,7 @@ static unsigned int __log2_64(uint64_t x) {
                  fprintf(stderr, "%.2f (s)", s->min / 1000000000.0);    \
              fprintf(stderr, "  max: ");                                \
              if (s->max < 1000)                                         \
-                 fprintf(stderr, "%lu (ns)", s->max);                   \
+                 fprintf(stderr, "%llu (ns)", s->max);                  \
              else if (s->max < 1000000)                                 \
                  fprintf(stderr, "%.2f (μs)", s->max / 1000.0);         \
              else if (s->max < 1000000000)                              \
diff --git a/c_src/wterl.c b/c_src/wterl.c
index fd21196..8756879 100644
--- a/c_src/wterl.c
+++ b/c_src/wterl.c
@@ -613,9 +613,9 @@ __wterl_progress_handler(WT_EVENT_HANDLER *handler, const char *operation, uint6
                       enif_make_int64(msg_env, counter)));
         enif_clear_env(msg_env);
         if (!enif_send(NULL, to_pid, msg_env, msg))
-            fprintf(stderr, "[%ld] %s\n", counter, operation);
+            fprintf(stderr, "[%llu] %s\n", counter, operation);
     } else {
-        rc = (printf("[%ld] %s\n", counter, operation) >= 0 ? 0 : EIO);
+        rc = (printf("[%llu] %s\n", counter, operation) >= 0 ? 0 : EIO);
     }
     enif_mutex_unlock(eh->progress_mutex);
     return rc;