diff --git a/m4/ax_pthread.m4 b/m4/ax_pthread.m4
index d90de34d1..e9787ce65 100644
--- a/m4/ax_pthread.m4
+++ b/m4/ax_pthread.m4
@@ -82,7 +82,7 @@
 #   modified version of the Autoconf Macro, you may extend this special
 #   exception to the GPL to apply to your modified version as well.
 
-#serial 18
+#serial 19
 
 AU_ALIAS([ACX_PTHREAD], [AX_PTHREAD])
 AC_DEFUN([AX_PTHREAD], [
@@ -159,8 +159,12 @@ case ${host_os} in
         ax_pthread_flags="-pthreads pthread -mt -pthread $ax_pthread_flags"
         ;;
 
+        darwin12*)
+        ax_pthread_flags="$ax_pthread_flags"
+        ;;
+
         darwin*)
-        ax_pthread_flags="-pthread $ax_pthread_flags"
+        ax_pthread_flags="-pthreads $ax_pthread_flags"
         ;;
 esac