Index: subversion/libsvn_ra_svn/marshal.c
===================================================================
--- subversion/libsvn_ra_svn/marshal.c	(revision 1767714)
+++ subversion/libsvn_ra_svn/marshal.c	(working copy)
@@ -913,6 +913,15 @@ vwrite_tuple_revision_opt(svn_ra_svn_conn_t *conn,
 }
 
 static svn_error_t *
+vwrite_tuple_number_opt(svn_ra_svn_conn_t *conn, apr_pool_t *pool, va_list *ap)
+{
+  apr_uint64_t number = va_arg(*ap, apr_uint64_t);
+  if (number != SVN_RA_SVN_UNSPECIFIED_NUMBER)
+    SVN_ERR(svn_ra_svn__write_number(conn, pool, va_arg(*ap, apr_uint64_t)));
+  return SVN_NO_ERROR;
+}
+
+static svn_error_t *
 vwrite_tuple_number(svn_ra_svn_conn_t *conn, apr_pool_t *pool, va_list *ap)
 {
   return svn_ra_svn__write_number(conn, pool, va_arg(*ap, apr_uint64_t));
@@ -1157,7 +1166,8 @@ static svn_error_t *vwrite_tuple(svn_ra_svn_conn_t
         SVN_ERR(opt ? vwrite_tuple_revision_opt(conn, pool, ap)
                     : vwrite_tuple_revision(conn, pool, ap));
       else if (*fmt == 'n' && !opt)
-        SVN_ERR(vwrite_tuple_number(conn, pool, ap));
+        SVN_ERR(opt ? vwrite_tuple_number_opt(conn, pool, ap)
+                    : vwrite_tuple_number(conn, pool, ap));
       else if (*fmt == 'b' && !opt)
         SVN_ERR(vwrite_tuple_boolean(conn, pool, ap));
       else if (*fmt == '!' && !*(fmt + 1))