diff -upk.orig less-394.orig/configure.ac less-394/configure.ac
--- less-394.orig/configure.ac	2005-10-21 16:21:55 +0000
+++ less-394/configure.ac	2007-03-31 16:37:19 +0000
@@ -14,6 +14,7 @@ AC_CONFIG_SRCDIR([forwback.c])
 AC_CONFIG_HEADER([defines.h])
 
 # Checks for programs.
+AC_GNU_SOURCE
 AC_PROG_CC
 AC_ISC_POSIX
 AC_PROG_GCC_TRADITIONAL