diff --git a/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php b/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
index e12023db52..33cbdc46e6 100644
--- a/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
+++ b/src/applications/calendar/editor/PhabricatorCalendarEventEditor.php
@@ -1,566 +1,594 @@
 <?php
 
 final class PhabricatorCalendarEventEditor
   extends PhabricatorApplicationTransactionEditor {
 
   public function getEditorApplicationClass() {
     return 'PhabricatorCalendarApplication';
   }
 
   public function getEditorObjectsDescription() {
     return pht('Calendar');
   }
 
   protected function shouldApplyInitialEffects(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return true;
   }
 
   protected function applyInitialEffects(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $actor = $this->requireActor();
     if ($object->getIsStub()) {
       $this->materializeStub($object);
     }
   }
 
   private function materializeStub(PhabricatorCalendarEvent $event) {
     if (!$event->getIsStub()) {
       throw new Exception(
         pht('Can not materialize an event stub: this event is not a stub.'));
     }
 
     $actor = $this->getActor();
     $event->copyFromParent($actor);
     $event->setIsStub(0);
 
     $invitees = $event->getParentEvent()->getInvitees();
 
     $new_invitees = array();
     foreach ($invitees as $invitee) {
       $invitee = id(new PhabricatorCalendarEventInvitee())
         ->setEventPHID($event->getPHID())
         ->setInviteePHID($invitee->getInviteePHID())
         ->setInviterPHID($invitee->getInviterPHID())
         ->setStatus($invitee->getStatus())
         ->save();
 
       $new_invitees[] = $invitee;
     }
 
     $event->save();
     $event->attachInvitees($new_invitees);
   }
 
   public function getTransactionTypes() {
     $types = parent::getTransactionTypes();
 
     $types[] = PhabricatorCalendarEventTransaction::TYPE_NAME;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_START_DATE;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_END_DATE;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_CANCEL;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_INVITE;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_ALL_DAY;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_ICON;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_ACCEPT;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_DECLINE;
 
     $types[] = PhabricatorCalendarEventTransaction::TYPE_RECURRING;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_FREQUENCY;
     $types[] = PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE;
 
     $types[] = PhabricatorTransactions::TYPE_COMMENT;
     $types[] = PhabricatorTransactions::TYPE_VIEW_POLICY;
     $types[] = PhabricatorTransactions::TYPE_EDIT_POLICY;
 
     return $types;
   }
 
   protected function getCustomTransactionOldValue(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     switch ($xaction->getTransactionType()) {
       case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
         return (int)$object->getIsRecurring();
       case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
         return $object->getFrequencyUnit();
       case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
         return $object->getRecurrenceEndDate();
       case PhabricatorCalendarEventTransaction::TYPE_NAME:
         return $object->getName();
       case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
         return $object->getDateFrom();
       case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
         return $object->getDateTo();
       case PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION:
         return $object->getDescription();
       case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
         return $object->getIsCancelled();
       case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
         return (int)$object->getIsAllDay();
       case PhabricatorCalendarEventTransaction::TYPE_ICON:
         return $object->getIcon();
       case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
       case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
         $actor_phid = $this->getActingAsPHID();
         return $object->getUserInviteStatus($actor_phid);
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
         $invitees = $object->getInvitees();
         return mpull($invitees, 'getStatus', 'getInviteePHID');
     }
 
     return parent::getCustomTransactionOldValue($object, $xaction);
   }
 
   protected function getCustomTransactionNewValue(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
     switch ($xaction->getTransactionType()) {
       case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
       case PhabricatorCalendarEventTransaction::TYPE_NAME:
       case PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION:
       case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
       case PhabricatorCalendarEventTransaction::TYPE_ICON:
         return $xaction->getNewValue();
       case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
         return PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
       case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
         return PhabricatorCalendarEventInvitee::STATUS_DECLINED;
       case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
       case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
         return (int)$xaction->getNewValue();
       case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
       case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
       case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
         return $xaction->getNewValue()->getEpoch();
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
         $status_invited = PhabricatorCalendarEventInvitee::STATUS_INVITED;
         $status_uninvited = PhabricatorCalendarEventInvitee::STATUS_UNINVITED;
         $status_attending = PhabricatorCalendarEventInvitee::STATUS_ATTENDING;
 
         $invitees = $object->getInvitees();
         foreach ($invitees as $key => $invitee) {
           if ($invitee->getStatus() == $status_uninvited) {
             unset($invitees[$key]);
           }
         }
         $invitees = mpull($invitees, null, 'getInviteePHID');
 
         $new = $xaction->getNewValue();
         $new = array_fuse($new);
 
         $all = array_keys($invitees + $new);
         $map = array();
         foreach ($all as $phid) {
           $is_old = isset($invitees[$phid]);
           $is_new = isset($new[$phid]);
 
           if ($is_old && !$is_new) {
             $map[$phid] = $status_uninvited;
           } else if (!$is_old && $is_new) {
             $map[$phid] = $status_invited;
           } else {
             $map[$phid] = $invitees[$phid]->getStatus();
           }
         }
 
         // If we're creating this event and the actor is inviting themselves,
         // mark them as attending.
         if ($this->getIsNewObject()) {
           $acting_phid = $this->getActingAsPHID();
           if (isset($map[$acting_phid])) {
             $map[$acting_phid] = $status_attending;
           }
         }
 
         return $map;
     }
 
     return parent::getCustomTransactionNewValue($object, $xaction);
   }
 
   protected function applyCustomInternalTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     switch ($xaction->getTransactionType()) {
       case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
         return $object->setIsRecurring((int)$xaction->getNewValue());
       case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
         return $object->setRecurrenceFrequency(
           array(
             'rule' => $xaction->getNewValue(),
           ));
       case PhabricatorCalendarEventTransaction::TYPE_NAME:
         $object->setName($xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
         $object->setDateFrom($xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
         $object->setDateTo($xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
         $object->setRecurrenceEndDate($xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION:
         $object->setDescription($xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
         $object->setIsCancelled((int)$xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
         $object->setIsAllDay((int)$xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_ICON:
         $object->setIcon($xaction->getNewValue());
         return;
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
       case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
       case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
         return;
     }
 
     return parent::applyCustomInternalTransaction($object, $xaction);
   }
 
   protected function applyCustomExternalTransaction(
     PhabricatorLiskDAO $object,
     PhabricatorApplicationTransaction $xaction) {
 
     switch ($xaction->getTransactionType()) {
       case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
       case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
       case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
       case PhabricatorCalendarEventTransaction::TYPE_NAME:
       case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
       case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
       case PhabricatorCalendarEventTransaction::TYPE_DESCRIPTION:
       case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
       case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
       case PhabricatorCalendarEventTransaction::TYPE_ICON:
         return;
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
         $map = $xaction->getNewValue();
         $phids = array_keys($map);
         $invitees = $object->getInvitees();
         $invitees = mpull($invitees, null, 'getInviteePHID');
 
         foreach ($phids as $phid) {
           $invitee = idx($invitees, $phid);
           if (!$invitee) {
             $invitee = id(new PhabricatorCalendarEventInvitee())
               ->setEventPHID($object->getPHID())
               ->setInviteePHID($phid)
               ->setInviterPHID($this->getActingAsPHID());
             $invitees[] = $invitee;
           }
           $invitee->setStatus($map[$phid])
             ->save();
         }
         $object->attachInvitees($invitees);
         return;
       case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
       case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
         $acting_phid = $this->getActingAsPHID();
 
         $invitees = $object->getInvitees();
         $invitees = mpull($invitees, null, 'getInviteePHID');
 
         $invitee = idx($invitees, $acting_phid);
         if (!$invitee) {
           $invitee = id(new PhabricatorCalendarEventInvitee())
             ->setEventPHID($object->getPHID())
             ->setInviteePHID($acting_phid)
             ->setInviterPHID($acting_phid);
           $invitees[$acting_phid] = $invitee;
         }
 
         $invitee
           ->setStatus($xaction->getNewValue())
           ->save();
 
         $object->attachInvitees($invitees);
         return;
     }
 
     return parent::applyCustomExternalTransaction($object, $xaction);
   }
 
   protected function applyFinalEffects(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     // Clear the availability caches for users whose availability is affected
     // by this edit.
 
     $invalidate_all = false;
     $invalidate_phids = array();
     foreach ($xactions as $xaction) {
       switch ($xaction->getTransactionType()) {
         case PhabricatorCalendarEventTransaction::TYPE_ICON:
           break;
         case PhabricatorCalendarEventTransaction::TYPE_RECURRING:
         case PhabricatorCalendarEventTransaction::TYPE_FREQUENCY:
         case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
         case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
         case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
         case PhabricatorCalendarEventTransaction::TYPE_CANCEL:
         case PhabricatorCalendarEventTransaction::TYPE_ALL_DAY:
           // For these kinds of changes, we need to invalidate the availabilty
           // caches for all attendees.
           $invalidate_all = true;
           break;
 
         case PhabricatorCalendarEventTransaction::TYPE_ACCEPT:
         case PhabricatorCalendarEventTransaction::TYPE_DECLINE:
           $acting_phid = $this->getActingAsPHID();
           $invalidate_phids[$acting_phid] = $acting_phid;
           break;
         case PhabricatorCalendarEventTransaction::TYPE_INVITE:
           foreach ($xaction->getNewValue() as $phid => $ignored) {
             $invalidate_phids[$phid] = $phid;
           }
           break;
       }
     }
 
     $phids = mpull($object->getInvitees(), 'getInviteePHID');
     $phids = array_fuse($phids);
 
     if (!$invalidate_all) {
       $phids = array_select_keys($phids, $invalidate_phids);
     }
 
     if ($phids) {
       $object->applyViewerTimezone($this->getActor());
 
       $user = new PhabricatorUser();
       $conn_w = $user->establishConnection('w');
       queryfx(
         $conn_w,
         'UPDATE %T SET availabilityCacheTTL = NULL
           WHERE phid IN (%Ls) AND availabilityCacheTTL >= %d',
         $user->getTableName(),
         $phids,
         $object->getDateFromForCache());
     }
 
     return $xactions;
   }
 
 
   protected function validateAllTransactions(
     PhabricatorLiskDAO $object,
     array $xactions) {
     $start_date_xaction =
       PhabricatorCalendarEventTransaction::TYPE_START_DATE;
     $end_date_xaction =
       PhabricatorCalendarEventTransaction::TYPE_END_DATE;
     $is_recurrence_xaction =
       PhabricatorCalendarEventTransaction::TYPE_RECURRING;
     $recurrence_end_xaction =
       PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE;
 
     $start_date = $object->getDateFrom();
     $end_date = $object->getDateTo();
     $recurrence_end = $object->getRecurrenceEndDate();
     $is_recurring = $object->getIsRecurring();
 
     $errors = array();
 
     foreach ($xactions as $xaction) {
       if ($xaction->getTransactionType() == $start_date_xaction) {
         $start_date = $xaction->getNewValue()->getEpoch();
       } else if ($xaction->getTransactionType() == $end_date_xaction) {
         $end_date = $xaction->getNewValue()->getEpoch();
       } else if ($xaction->getTransactionType() == $recurrence_end_xaction) {
         $recurrence_end = $xaction->getNewValue()->getEpoch();
       } else if ($xaction->getTransactionType() == $is_recurrence_xaction) {
         $is_recurring = $xaction->getNewValue();
       }
     }
 
     if ($start_date > $end_date) {
       $type = PhabricatorCalendarEventTransaction::TYPE_END_DATE;
       $errors[] = new PhabricatorApplicationTransactionValidationError(
         $type,
         pht('Invalid'),
         pht('End date must be after start date.'),
         null);
     }
 
     if ($recurrence_end && !$is_recurring) {
       $type =
         PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE;
       $errors[] = new PhabricatorApplicationTransactionValidationError(
         $type,
         pht('Invalid'),
         pht('Event must be recurring to have a recurrence end date.').
         null);
     }
 
     return $errors;
   }
 
   protected function validateTransaction(
     PhabricatorLiskDAO $object,
     $type,
     array $xactions) {
 
     $errors = parent::validateTransaction($object, $type, $xactions);
 
     switch ($type) {
       case PhabricatorCalendarEventTransaction::TYPE_NAME:
         $missing = $this->validateIsEmptyTextField(
           $object->getName(),
           $xactions);
 
         if ($missing) {
           $error = new PhabricatorApplicationTransactionValidationError(
             $type,
             pht('Required'),
             pht('Event name is required.'),
             nonempty(last($xactions), null));
 
           $error->setIsMissingFieldError(true);
           $errors[] = $error;
         }
         break;
       case PhabricatorCalendarEventTransaction::TYPE_INVITE:
         $old = $object->getInvitees();
         $old = mpull($old, null, 'getInviteePHID');
         foreach ($xactions as $xaction) {
           $new = $xaction->getNewValue();
           $new = array_fuse($new);
           $add = array_diff_key($new, $old);
           if (!$add) {
             continue;
           }
 
           // In the UI, we only allow you to invite mailable objects, but there
           // is no definitive marker for "invitable object" today. Just allow
           // any valid object to be invited.
           $objects = id(new PhabricatorObjectQuery())
             ->setViewer($this->getActor())
             ->withPHIDs($add)
             ->execute();
           $objects = mpull($objects, null, 'getPHID');
           foreach ($add as $phid) {
             if (isset($objects[$phid])) {
               continue;
             }
 
             $errors[] = new PhabricatorApplicationTransactionValidationError(
               $type,
               pht('Invalid'),
               pht(
                 'Invitee "%s" identifies an object that does not exist or '.
                 'which you do not have permission to view.',
                 $phid));
           }
         }
         break;
+      case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
+      case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
+      case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
+        foreach ($xactions as $xaction) {
+          if ($xaction->getNewValue()->isValid()) {
+            continue;
+          }
+
+          switch ($type) {
+            case PhabricatorCalendarEventTransaction::TYPE_START_DATE:
+              $message = pht('Start date is invalid.');
+              break;
+            case PhabricatorCalendarEventTransaction::TYPE_END_DATE:
+              $message = pht('End date is invalid.');
+              break;
+            case PhabricatorCalendarEventTransaction::TYPE_RECURRENCE_END_DATE:
+              $message = pht('Repeat until date is invalid.');
+              break;
+          }
+
+          $errors[] = new PhabricatorApplicationTransactionValidationError(
+            $type,
+            pht('Invalid'),
+            $message,
+            $xaction);
+        }
+        break;
+
     }
 
     return $errors;
   }
 
   protected function shouldPublishFeedStory(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return true;
   }
 
   protected function supportsSearch() {
     return true;
   }
 
   protected function shouldSendMail(
     PhabricatorLiskDAO $object,
     array $xactions) {
     return true;
   }
 
   protected function getMailSubjectPrefix() {
     return pht('[Calendar]');
   }
 
   protected function getMailTo(PhabricatorLiskDAO $object) {
     $phids = array();
 
     if ($object->getUserPHID()) {
       $phids[] = $object->getUserPHID();
     }
     $phids[] = $this->getActingAsPHID();
 
     $invitees = $object->getInvitees();
     foreach ($invitees as $invitee) {
       $status = $invitee->getStatus();
       if ($status === PhabricatorCalendarEventInvitee::STATUS_ATTENDING
         || $status === PhabricatorCalendarEventInvitee::STATUS_INVITED) {
         $phids[] = $invitee->getInviteePHID();
       }
     }
 
     $phids = array_unique($phids);
 
     return $phids;
   }
 
   public function getMailTagsMap() {
     return array(
       PhabricatorCalendarEventTransaction::MAILTAG_CONTENT =>
         pht(
           "An event's name, status, invite list, ".
           "icon, and description changes."),
       PhabricatorCalendarEventTransaction::MAILTAG_RESCHEDULE =>
         pht(
           "An event's start and end date ".
           "and cancellation status changes."),
       PhabricatorCalendarEventTransaction::MAILTAG_OTHER =>
         pht('Other event activity not listed above occurs.'),
     );
   }
 
   protected function buildReplyHandler(PhabricatorLiskDAO $object) {
     return id(new PhabricatorCalendarReplyHandler())
       ->setMailReceiver($object);
   }
 
   protected function buildMailTemplate(PhabricatorLiskDAO $object) {
     $id = $object->getID();
     $name = $object->getName();
 
     return id(new PhabricatorMetaMTAMail())
       ->setSubject("E{$id}: {$name}")
       ->addHeader('Thread-Topic', "E{$id}: ".$object->getName());
   }
 
   protected function buildMailBody(
     PhabricatorLiskDAO $object,
     array $xactions) {
 
     $description = $object->getDescription();
     $body = parent::buildMailBody($object, $xactions);
 
     if (strlen($description)) {
       $body->addRemarkupSection(
         pht('EVENT DESCRIPTION'),
         $description);
     }
 
     $body->addLinkSection(
       pht('EVENT DETAIL'),
       PhabricatorEnv::getProductionURI('/E'.$object->getID()));
 
 
     return $body;
   }
 
 
 }