Index: src/chrono.cpp
===================================================================
--- src/chrono.cpp
+++ src/chrono.cpp
@@ -8,15 +8,22 @@
 //===----------------------------------------------------------------------===//
 
 #include "chrono"
-#include <sys/time.h>        //for gettimeofday and timeval
-#ifdef __APPLE__
-#include <mach/mach_time.h>  // mach_absolute_time, mach_timebase_info_data_t
-#else  /* !__APPLE__ */
 #include <cerrno>  // errno
 #include <system_error>  // __throw_system_error
-#include <time.h>  // clock_gettime, CLOCK_MONOTONIC
-#endif  // __APPLE__
+#include <time.h>  // clock_gettime, CLOCK_MONOTONIC and CLOCK_REALTIME
 
+#if !defined(CLOCK_REALTIME)
+#include <sys/time.h>        // for gettimeofday and timeval
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_MONOTONIC_CLOCK) && !defined(CLOCK_MONOTONIC)
+#if __APPLE__
+#include <mach/mach_time.h>  // mach_absolute_time, mach_timebase_info_data_t
+#else
+#error "Monotonic clock not implemented"
+#endif
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace chrono
@@ -29,9 +36,16 @@
 system_clock::time_point
 system_clock::now() _NOEXCEPT
 {
+#ifdef CLOCK_REALTIME
+    struct timespec tp;
+    if (0 != clock_gettime(CLOCK_REALTIME, &tp))
+        __throw_system_error(errno, "clock_gettime(CLOCK_REALTIME) failed");
+    return time_point(seconds(tp.tv_sec) + microseconds(tp.tv_nsec / 1000));
+#else  // !CLOCK_REALTIME
     timeval tv;
     gettimeofday(&tv, 0);
     return time_point(seconds(tv.tv_sec) + microseconds(tv.tv_usec));
+#endif  // CLOCK_REALTIME
 }
 
 time_t
@@ -48,10 +62,26 @@
 
 #ifndef _LIBCPP_HAS_NO_MONOTONIC_CLOCK
 // steady_clock
+//
+// Warning:  If this is not truly steady, then it is non-conforming.  It is
+//  better for it to not exist and have the rest of libc++ use system_clock
+//  instead.
 
 const bool steady_clock::is_steady;
 
-#ifdef __APPLE__
+#ifdef CLOCK_MONOTONIC
+
+steady_clock::time_point
+steady_clock::now() _NOEXCEPT
+{
+    struct timespec tp;
+    if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
+        __throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
+    return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
+}
+
+#elif defined(__APPLE__)
+
 //   mach_absolute_time() * MachInfo.numer / MachInfo.denom is the number of
 //   nanoseconds since the computer booted up.  MachInfo.numer and MachInfo.denom
 //   are run time constants supplied by the OS.  This clock has no relationship
@@ -108,24 +138,10 @@
     return time_point(duration(fp()));
 }
 
-#else  // __APPLE__
-// FIXME: if _LIBCPP_HAS_NO_MONOTONIC_CLOCK, then clock_gettime isn't going to
-// work. It may be possible to fall back on something else, depending on the system.
+#else
+#error "Monotonic clock not implemented"
+#endif
 
-// Warning:  If this is not truly steady, then it is non-conforming.  It is
-//  better for it to not exist and have the rest of libc++ use system_clock
-//  instead.
-
-steady_clock::time_point
-steady_clock::now() _NOEXCEPT
-{
-    struct timespec tp;
-    if (0 != clock_gettime(CLOCK_MONOTONIC, &tp))
-        __throw_system_error(errno, "clock_gettime(CLOCK_MONOTONIC) failed");
-    return time_point(seconds(tp.tv_sec) + nanoseconds(tp.tv_nsec));
-}
-#endif  // __APPLE__
-
 #endif // !_LIBCPP_HAS_NO_MONOTONIC_CLOCK
 
 }