diff --git a/m4/xstrtod.m4 b/m4/xstrtod.m4
index 9307bd391..e9c94ca68 100644
--- a/m4/xstrtod.m4
+++ b/m4/xstrtod.m4
@@ -1,5 +1,5 @@
-#serial 4
-dnl Copyright (C) 2002, 2003, 2005 Free Software Foundation, Inc.
+#serial 5
+dnl Copyright (C) 2002, 2003, 2005, 2006 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
@@ -10,3 +10,10 @@ AC_DEFUN([gl_XSTRTOD],
   AC_LIBSOURCES([xstrtod.c, xstrtod.h])
   AC_LIBOBJ([xstrtod])
 ])
+
+# Prerequisites of lib/xstrtold.c.
+AC_DEFUN([gl_XSTRTOLD],
+[
+  AC_LIBSOURCES([xstrtold.c, xstrtod.c, xstrtod.h])
+  AC_LIBOBJ([xstrtold])
+])