Index: flex-2.6.4/configure.ac
===================================================================
--- flex-2.6.4.orig/configure.ac
+++ flex-2.6.4/configure.ac
@@ -27,6 +27,7 @@
 AC_INIT([the fast lexical analyser generator],[2.6.4],[flex-help@lists.sourceforge.net],[flex])
 AC_CONFIG_SRCDIR([src/scan.l])
 AC_CONFIG_AUX_DIR([build-aux])
+AC_USE_SYSTEM_EXTENSIONS
 LT_INIT
 AM_INIT_AUTOMAKE([1.11.3 -Wno-portability foreign check-news std-options dist-lzip parallel-tests subdir-objects])
 AC_CONFIG_HEADER([src/config.h])