diff --git a/libguile/posix.c b/libguile/posix.c
index d27bbbc00..ed5ae2be2 100644
--- a/libguile/posix.c
+++ b/libguile/posix.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001,2002,2004 Free Software Foundation, Inc.
+/* Copyright (C) 1995,1996,1997,1998,1999,2000,2001,2002,2004, 2005 Free Software Foundation, Inc.
  * 
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -1295,7 +1295,13 @@ SCM_DEFINE (scm_setlocale, "setlocale", 1, 1, 0,
 
   rv = setlocale (SCM_INUM (category), clocale);
   if (rv == NULL)
-    SCM_SYSERROR;
+    {
+      /* POSIX and C99 don't say anything about setlocale setting errno, so
+         force a sensible value here.  glibc leaves ENOENT, which would be
+         fine, but it's not a documented feature.  */
+      errno = EINVAL;
+      SCM_SYSERROR;
+    }
   return scm_makfrom0str (rv);
 }
 #undef FUNC_NAME