$OpenBSD$
--- configure.in.orig	Thu Jan  5 11:09:48 2006
+++ configure.in	Thu Jan  5 11:10:33 2006
@@ -88,6 +88,9 @@ AC_CHECK_HEADERS([linux/netfilter_ipv4.h
    #endif
    ]] )
 
+AC_CHECK_HEADERS([net/pfvar.h],
+       AC_DEFINE(USE_PF_NATLOOKUP, 1, [Whether the system supports OpenBSD packet filter for transparent proxy]),,)
+
 # Checks for typedefs, structures, and compiler characteristics.
 AC_C_CONST
 AC_TYPE_SIZE_T
