diff --git a/booking.variety_form.inc b/booking.variety_form.inc
index e958002..2aca303 100644
--- a/booking.variety_form.inc
+++ b/booking.variety_form.inc
@@ -131,6 +131,8 @@ function booking_variety_regn_form_validate($form, &$form_state) {
     return;
   }
 
+  // --- Check that the registration number is valid ---
+
   //verify that user-entered data is a number
   if (! preg_match('/^[0-9]+$/', $values['booking_nid'])) {
     form_set_error('booking_nid', t('You have entered an invalid booking reference number.'));
@@ -152,6 +154,14 @@ function booking_variety_regn_form_validate($form, &$form_state) {
     form_set_error('booking_nid', t('You have entered an invalid booking reference number.'));
   }
 
+  // --- Check that this person hasn't already registered for variety sessions
+  $query_already_registered = db_query("SELECT * FROM {booking_variety_regn} WHERE booking_person_nid = :nid", 
+    array(':nid' => $values['booking_nid']));
+
+  if ($query_already_registered) {
+    form_set_error('booking_nid', t('You have already registered for variety sessions.'));
+  }
+
   // --- Check there is still space available in the selected variety sessions ---
 
   //get a list of timeslot IDs from matching form values