--- loncom/interface/lonnavmaps.pm	2006/06/29 16:32:14	1.389
+++ loncom/interface/lonnavmaps.pm	2006/07/25 00:57:51	1.390
@@ -1,7 +1,7 @@
 # The LearningOnline Network with CAPA
 # Navigate Maps Handler
 #
-# $Id: lonnavmaps.pm,v 1.389 2006/06/29 16:32:14 albertel Exp $
+# $Id: lonnavmaps.pm,v 1.390 2006/07/25 00:57:51 albertel Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -4046,7 +4046,7 @@ sub duedate {
     my $date;
     my $interval=$self->parmval("interval", $part);
     my $due_date=$self->parmval("duedate", $part);
-    if (defined($interval)) {
+    if ($interval =~ /\d+/) {
 	my $first_access=&Apache::lonnet::get_first_access('map',$self->symb);
 	if (defined($first_access)) {
 	    $interval = $first_access+$interval;