diff --git a/src/applications/harbormaster/worker/HarbormasterTargetWorker.php b/src/applications/harbormaster/worker/HarbormasterTargetWorker.php
index fa3a01272b..a6860f579c 100644
--- a/src/applications/harbormaster/worker/HarbormasterTargetWorker.php
+++ b/src/applications/harbormaster/worker/HarbormasterTargetWorker.php
@@ -1,112 +1,118 @@
 <?php
 
 /**
  * Execute a build target.
  */
 final class HarbormasterTargetWorker extends HarbormasterWorker {
 
   public function getRequiredLeaseTime() {
     // This worker performs actual build work, which may involve a long wait
     // on external systems.
     return phutil_units('24 hours in seconds');
   }
 
   public function renderForDisplay(PhabricatorUser $viewer) {
     try {
       $target = $this->loadBuildTarget();
     } catch (Exception $ex) {
       return null;
     }
 
     return $viewer->renderHandle($target->getPHID());
   }
 
   private function loadBuildTarget() {
     $data = $this->getTaskData();
     $id = idx($data, 'targetID');
 
     $target = id(new HarbormasterBuildTargetQuery())
       ->withIDs(array($id))
       ->setViewer($this->getViewer())
       ->needBuildSteps(true)
       ->executeOne();
 
     if (!$target) {
       throw new PhabricatorWorkerPermanentFailureException(
         pht(
           'Bad build target ID "%d".',
           $id));
     }
 
     return $target;
   }
 
   protected function doWork() {
     $target = $this->loadBuildTarget();
     $build = $target->getBuild();
     $viewer = $this->getViewer();
 
-    $target->setDateStarted(time());
+    // If this is the first time we're starting work on this target, mark the
+    // current time as the start time. If the target yields or waits, we may
+    // end up here again later, so we don't want to overwrite the start time if
+    // we already have a value.
+    if (!$target->getDateStarted()) {
+      $target->setDateStarted(PhabricatorTime::getNow());
+    }
 
     try {
       if ($target->getBuildGeneration() !== $build->getBuildGeneration()) {
         throw new HarbormasterBuildAbortedException();
       }
 
       $status_pending = HarbormasterBuildTarget::STATUS_PENDING;
       if ($target->getTargetStatus() == $status_pending) {
         $target->setTargetStatus(HarbormasterBuildTarget::STATUS_BUILDING);
         $target->save();
       }
 
       $implementation = $target->getImplementation();
       $implementation->setCurrentWorkerTaskID($this->getCurrentWorkerTaskID());
       $implementation->execute($build, $target);
 
       $next_status = HarbormasterBuildTarget::STATUS_PASSED;
       if ($implementation->shouldWaitForMessage($target)) {
         $next_status = HarbormasterBuildTarget::STATUS_WAITING;
       }
 
       $target->setTargetStatus($next_status);
 
       if ($target->isComplete()) {
         $target->setDateCompleted(PhabricatorTime::getNow());
       }
 
       $target->save();
     } catch (PhabricatorWorkerYieldException $ex) {
       // If the target wants to yield, let that escape without further
       // processing. We'll resume after the task retries.
       throw $ex;
     } catch (HarbormasterBuildFailureException $ex) {
       // A build step wants to fail explicitly.
       $target->setTargetStatus(HarbormasterBuildTarget::STATUS_FAILED);
       $target->setDateCompleted(PhabricatorTime::getNow());
       $target->save();
     } catch (HarbormasterBuildAbortedException $ex) {
       // A build step is aborting because the build has been restarted.
       $target->setTargetStatus(HarbormasterBuildTarget::STATUS_ABORTED);
       $target->setDateCompleted(PhabricatorTime::getNow());
       $target->save();
     } catch (Exception $ex) {
       try {
         $log = $target->newLog('core', 'exception')
           ->append($ex)
           ->closeBuildLog();
       } catch (Exception $log_ex) {
         phlog($log_ex);
       }
 
       $target->setTargetStatus(HarbormasterBuildTarget::STATUS_FAILED);
       $target->setDateCompleted(time());
       $target->save();
     }
 
     id(new HarbormasterBuildEngine())
       ->setViewer($viewer)
       ->setBuild($build)
       ->continueBuild();
   }
 
 }