diff --git a/booking.rooms_admin.inc b/booking.rooms_admin.inc
index 3da20e9..0790d08 100644
--- a/booking.rooms_admin.inc
+++ b/booking.rooms_admin.inc
@@ -432,10 +432,13 @@ function booking_rooms_definition_form_validate($form, $form_state) {
 	//make sure room number is numerical
 	$values = $form_state['input'];
 
-	if ((! is_numeric($values['booking_room_number'])) && $form_state['values']['op'] != 'Delete Room') {
-		form_set_error('booking_room_number', t('Room number must be numeric. If you need to use a more descriptive label, please use the room label field.'));
-		watchdog('booking_debug', "<pre>Room definition submission:\n@info</pre>", array('@info' => print_r( $form_state, true)));
+	if ($form_state['values']['op'] != 'Delete Room') {
+		if (isset($values['booking_room_number']) && (! is_numeric($values['booking_room_number']))) {
+			form_set_error('booking_room_number', t('Room number must be numeric. If you need to use a more descriptive label, please use the room label field.'));
+			watchdog('booking_debug', "<pre>Room definition submission:\n@info</pre>", array('@info' => print_r( $form_state, true)));
+		}
 	}
+
 }
 
 /**