--- ./xl2tpd.c.orig
+++ ./xl2tpd.c
@@ -30,7 +30,7 @@
 #include <errno.h>
 #include <unistd.h>
 #include <time.h>
-#if (__GLIBC__ < 2)
+#if defined(__GLIBC__) && (__GLIBC__ < 2)
 # if defined(FREEBSD) || defined(OPENBSD)
 #  include <sys/signal.h>
 # elif defined(LINUX)