diff --git a/booking.variety_form.inc b/booking.variety_form.inc
index 9828e4d..a420fe8 100644
--- a/booking.variety_form.inc
+++ b/booking.variety_form.inc
@@ -167,6 +167,13 @@ function booking_variety_regn_form_validate($form, &$form_state) {
   //check there is still room 
   foreach ($variety_timeslot_ids as $id) {
     $selected_session_id = $values['select-variety-' . $id];
+
+    // Don't try and check availablity for a select element that is still on the default value
+    if ($selected_session_id == 0) {
+      form_set_error('select-variety-' . $id, t('You have not selected a variety session.'));
+      continue;
+    }
+
     $session = $sessions[$selected_session_id];
     if ($session->booking_variety_regncount < $session->booking_variety_maxsize) {
       watchdog('booking_debug', 'Still room in session @id : @count is less than @size', array(