new file mode 100644
--- /dev/null
+++ b/m4/memmem.m4
@@ -0,0 +1,20 @@
+# memmem.m4 serial 1
+dnl Copyright (C) 2002, 2003, 2004 Free Software Foundation, Inc.
+dnl This file is free software, distributed under the terms of the GNU
+dnl General Public License.  As a special exception to the GNU General
+dnl Public License, this file may be distributed as part of a program
+dnl that contains a configuration script generated by Autoconf, under
+dnl the same distribution terms as the rest of that program.
+
+AC_DEFUN([gl_FUNC_MEMMEM],
+[
+  dnl Persuade glibc <string.h> to declare memmem().
+  AC_REQUIRE([AC_GNU_SOURCE])
+
+  AC_REPLACE_FUNCS(memmem)
+  AC_CHECK_DECLS_ONCE(memmem)
+  gl_PREREQ_MEMMEM
+])
+
+# Prerequisites of lib/memmem.c.
+AC_DEFUN([gl_PREREQ_MEMMEM], [:])