diff --git a/configure.ac b/configure.ac
index 242919a19..b450ff955 100644
--- a/configure.ac
+++ b/configure.ac
@@ -471,6 +471,7 @@ EOF
 fi
 if test "x$have_darwin" = "xyes"; then
     AC_DEFINE([HAVE_DARWIN], 1)
+    AC_DEFINE([SYS_DARWIN], 1)
 fi
 if test "x$have_msw" = "xyes"; then
     AC_DEFINE([HAVE_MSW], 1)