diff --git a/reproc/src/clock.posix.c b/reproc/src/clock.posix.c
index 8d22a3b..4d47fa3 100644
--- a/reproc/src/clock.posix.c
+++ b/reproc/src/clock.posix.c
@@ -6,11 +6,39 @@
 
 #include "error.h"
 
+#if defined __APPLE__ && __MAC_OS_X_VERSION_MIN_REQUIRED < 101200 // less than macOS 10.12
+#include <Availability.h>
+  #ifndef CLOCK_REALTIME
+  #define CLOCK_REALTIME 0
+  #endif
+
+  #include <mach/clock.h>
+  #include <mach/mach.h>
+  #include <sys/time.h>
+
+  int alt_clock_gettime (int clock_id, struct timespec *ts)
+  {
+    clock_serv_t cclock;
+    mach_timespec_t mts;
+    host_get_clock_service (mach_host_self (), clock_id, &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;
+    return 0;
+  }
+#endif
+
+
 int64_t now(void)
 {
   struct timespec timespec = { 0 };
 
+#if defined __APPLE__ && __MAC_OS_X_VERSION_MIN_REQUIRED < 101200 // less than macOS 10.12
+  int r = alt_clock_gettime(CLOCK_REALTIME, &timespec);
+#else
   int r = clock_gettime(CLOCK_REALTIME, &timespec);
+#endif
   ASSERT_UNUSED(r == 0);
 
   return timespec.tv_sec * 1000 + timespec.tv_nsec / 1000000;