if_tun_h="\"$kerneldir/include/linux/if_tun.h\"",
[AC_TRY_COMPILE([#include <linux/if_tun.h>],
[int a = IFF_TAP;],
if_tun_h="\"$kerneldir/include/linux/if_tun.h\"",
[AC_TRY_COMPILE([#include <linux/if_tun.h>],
[int a = IFF_TAP;],
- AC_DEFINE_UNQUOTED(LINUX_IF_TUN_H, $tinc_cv_linux_if_tun_h)
- AC_SUBST(LINUX_IF_TUN_H)
+ if test $tinc_cv_linux_if_tun_h != default; then
+ AC_DEFINE_UNQUOTED(LINUX_IF_TUN_H, $tinc_cv_linux_if_tun_h)
+ fi