diff --git a/configure.in b/configure.in
index 797cc3b19..a875edcf9 100644
--- a/configure.in
+++ b/configure.in
@@ -734,10 +734,12 @@ AC_CHECK_FUNCS([DINFINITY DQNAN cexp chsize clog clog10 ctermid fesetround ftime
 #       declaration is only found if `_BSD' is defined; it's marked as
 #       discouraged in <stdlib.h> and has type `void' instead of `int'
 #       anyway.
+#   hstrerror - on Tru64 5.1b the symbol is available in libc but the
+#       declaration isn't anywhere.
 #
 AC_CHECK_HEADERS(crypt.h netdb.h pthread.h sys/param.h sys/resource.h sys/file.h)
 AC_CHECK_FUNCS(chroot flock getlogin cuserid getpriority setpriority getpass sethostname gethostname)
-AC_CHECK_DECLS([sethostname, strncasecmp, unsetenv])
+AC_CHECK_DECLS([sethostname, strncasecmp, unsetenv, hstrerror])
 
 # crypt() may or may not be available, for instance in some countries there
 # are restrictions on cryptography.
diff --git a/libguile/net_db.c b/libguile/net_db.c
index deb8d381d..af6e3d5f4 100644
--- a/libguile/net_db.c
+++ b/libguile/net_db.c
@@ -1,5 +1,5 @@
 /* "net_db.c" network database support
- * Copyright (C) 1995,1996,1997,1998,1999,2000,2001, 2006 Free Software Foundation, Inc.
+ * Copyright (C) 1995,1996,1997,1998,1999,2000,2001, 2006, 2009 Free Software Foundation, Inc.
  * 
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ -64,6 +64,12 @@
 extern int h_errno;
 #endif
 
+#if defined HAVE_HSTRERROR && !HAVE_DECL_HSTRERROR	\
+  && !defined __MINGW32__ && !defined __CYGWIN__
+/* Some OSes, such as Tru64 5.1b, lack a declaration for hstrerror(3).  */
+extern const char *hstrerror (int);
+#endif
+
 
 
 SCM_SYMBOL (scm_host_not_found_key, "host-not-found");