diff --git a/src/os_unix.c b/src/os_unix.c
index cc02653..80459c9 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -804,6 +804,12 @@
  * completely full.
  */
 
+#if defined(HAVE_AVAILABILITYMACROS_H) \
+    && defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) \
+    && (__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ >= 1090)
+# include <AvailabilityMacros.h>
+#endif
+
 #ifndef SIGSTKSZ
 # define SIGSTKSZ 8000    /* just a guess of how much stack is needed... */
 #endif