diff --git a/configure.ac b/configure.ac
index ec62785c0..2c0738d8d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -87,7 +87,7 @@ case $host_os in
     darwin*)
 	if test x$enable_x11 = xyes; then
 		host_os_gui="X11"
-		OPTIM="-U__APPLE__ -mmacosx-version-min=10.3 $OPTIM"
+		OPTIM="-U__APPLE__ -mmacosx-version-min=10.9 -D_LIBCPP_HAS_THREAD_API_PTHREAD $OPTIM"
 	fi
 	;;
    *)