diff --git a/js/src/old-configure.in b/js/src/old-configure.in
index f0e88431754c..b1a75c8cd3f2 100644
--- a/js/src/old-configure.in
+++ b/js/src/old-configure.in
@@ -1003,35 +1003,31 @@ dnl ========================================================
 AC_CHECK_FUNCS([getc_unlocked _getc_nolock gmtime_r localtime_r pthread_getname_np pthread_get_name_np])
 
 dnl check for clock_gettime(), the CLOCK_MONOTONIC clock
-dnl avoid this on Darwin, since depending on your system config, we may think
-dnl it exists but it really doesn't
-case "$OS_TARGET" in
-Darwin)
-  ;;
-*)
-  AC_CACHE_CHECK(for clock_gettime(CLOCK_MONOTONIC),
-                 ac_cv_clock_monotonic,
-                 [for libs in "" -lrt; do
-                      _SAVE_LIBS="$LIBS"
-                      LIBS="$LIBS $libs"
-                      AC_TRY_LINK([#include <time.h>],
-                                   [ struct timespec ts;
-                                     clock_gettime(CLOCK_MONOTONIC, &ts); ],
-                                   ac_cv_clock_monotonic=$libs
-                                   LIBS="$_SAVE_LIBS"
-                                   break,
-                                   ac_cv_clock_monotonic=no)
-                      LIBS="$_SAVE_LIBS"
-                  done])
-  if test "$ac_cv_clock_monotonic" != "no"; then
-      HAVE_CLOCK_MONOTONIC=1
-      REALTIME_LIBS=$ac_cv_clock_monotonic
-      AC_DEFINE(HAVE_CLOCK_MONOTONIC)
-      AC_SUBST(HAVE_CLOCK_MONOTONIC)
-      AC_SUBST_LIST(REALTIME_LIBS)
-  fi
-  ;;
-esac
+AC_CACHE_CHECK(for clock_gettime(CLOCK_MONOTONIC),
+               ac_cv_clock_monotonic,
+               [for libs in "" -lrt; do
+                    _SAVE_LIBS="$LIBS"
+                    LIBS="$LIBS $libs"
+dnl clock_gettime is available on OSX since 10.12, so depending on MACOSX_DEPLOYMENT_TARGET,
+dnl we should or not be able to use it. To detect if we can, we need to make the
+dnl availability attribute strict, so that compilation fails when the target is < 10.12.
+                    AC_TRY_LINK([#define availability(os, ...) availability(os, strict, __VA_ARGS)
+                                 #include <time.h>],
+                                 [ struct timespec ts;
+                                   clock_gettime(CLOCK_MONOTONIC, &ts); ],
+                                 ac_cv_clock_monotonic=$libs
+                                 LIBS="$_SAVE_LIBS"
+                                 break,
+                                 ac_cv_clock_monotonic=no)
+                    LIBS="$_SAVE_LIBS"
+                done])
+if test "$ac_cv_clock_monotonic" != "no"; then
+    HAVE_CLOCK_MONOTONIC=1
+    REALTIME_LIBS=$ac_cv_clock_monotonic
+    AC_DEFINE(HAVE_CLOCK_MONOTONIC)
+    AC_SUBST(HAVE_CLOCK_MONOTONIC)
+    AC_SUBST_LIST(REALTIME_LIBS)
+fi
 
 dnl Checks for math functions.
 dnl ========================================================
diff --git a/old-configure.in b/old-configure.in
index 1db63f3ef188..e7283611b92e 100644
--- a/old-configure.in
+++ b/old-configure.in
@@ -1278,35 +1278,31 @@ dnl ========================================================
 AC_CHECK_FUNCS(stat64 lstat64 truncate64 statvfs64 statvfs statfs64 statfs getpagesize gmtime_r localtime_r arc4random arc4random_buf mallinfo gettid lchown setpriority strerror syscall)
 
 dnl check for clock_gettime(), the CLOCK_MONOTONIC clock
-dnl avoid this on Darwin, since depending on your system config, we may think
-dnl it exists but it really doesn't
-case "$OS_TARGET" in
-Darwin)
-  ;;
-*)
-  AC_CACHE_CHECK(for clock_gettime(CLOCK_MONOTONIC),
-                 ac_cv_clock_monotonic,
-                 [for libs in "" -lrt; do
-                      _SAVE_LIBS="$LIBS"
-                      LIBS="$LIBS $libs"
-                      AC_TRY_LINK([#include <time.h>],
-                                   [ struct timespec ts;
-                                     clock_gettime(CLOCK_MONOTONIC, &ts); ],
-                                   ac_cv_clock_monotonic=$libs
-                                   LIBS="$_SAVE_LIBS"
-                                   break,
-                                   ac_cv_clock_monotonic=no)
-                      LIBS="$_SAVE_LIBS"
-                  done])
-  if test "$ac_cv_clock_monotonic" != "no"; then
-      HAVE_CLOCK_MONOTONIC=1
-      REALTIME_LIBS=$ac_cv_clock_monotonic
-      AC_DEFINE(HAVE_CLOCK_MONOTONIC)
-      AC_SUBST(HAVE_CLOCK_MONOTONIC)
-      AC_SUBST_LIST(REALTIME_LIBS)
-  fi
-  ;;
-esac
+AC_CACHE_CHECK(for clock_gettime(CLOCK_MONOTONIC),
+               ac_cv_clock_monotonic,
+               [for libs in "" -lrt; do
+                    _SAVE_LIBS="$LIBS"
+                    LIBS="$LIBS $libs"
+dnl clock_gettime is available on OSX since 10.12, so depending on MACOSX_DEPLOYMENT_TARGET,
+dnl we should or not be able to use it. To detect if we can, we need to make the
+dnl availability attribute strict, so that compilation fails when the target is < 10.12.
+                    AC_TRY_LINK([#define availability(os, ...) availability(os, strict, __VA_ARGS)
+                                 #include <time.h>],
+                                 [ struct timespec ts;
+                                   clock_gettime(CLOCK_MONOTONIC, &ts); ],
+                                 ac_cv_clock_monotonic=$libs
+                                 LIBS="$_SAVE_LIBS"
+                                 break,
+                                 ac_cv_clock_monotonic=no)
+                    LIBS="$_SAVE_LIBS"
+                done])
+if test "$ac_cv_clock_monotonic" != "no"; then
+    HAVE_CLOCK_MONOTONIC=1
+    REALTIME_LIBS=$ac_cv_clock_monotonic
+    AC_DEFINE(HAVE_CLOCK_MONOTONIC)
+    AC_SUBST(HAVE_CLOCK_MONOTONIC)
+    AC_SUBST_LIST(REALTIME_LIBS)
+fi
 
 dnl Turn on warnings-as-errors to prevent implicit declaration of
 dnl pthread_cond_timedwait_monotonic_np, which can cause this test to