diff --git a/src/applications/harbormaster/step/HarbormasterWaitForPreviousBuildStepImplementation.php b/src/applications/harbormaster/step/HarbormasterWaitForPreviousBuildStepImplementation.php
index 6cfa0759fa..1c54525064 100644
--- a/src/applications/harbormaster/step/HarbormasterWaitForPreviousBuildStepImplementation.php
+++ b/src/applications/harbormaster/step/HarbormasterWaitForPreviousBuildStepImplementation.php
@@ -1,102 +1,102 @@
 <?php
 
 final class HarbormasterWaitForPreviousBuildStepImplementation
   extends HarbormasterBuildStepImplementation {
 
   public function getName() {
     return pht('Wait for Previous Commits to Build');
   }
 
   public function getGenericDescription() {
     return pht(
       'Wait for previous commits to finish building the current plan '.
       'before continuing.');
   }
 
   public function execute(
     HarbormasterBuild $build,
     HarbormasterBuildTarget $build_target) {
 
     // We can only wait when building against commits.
     $buildable = $build->getBuildable();
     $object = $buildable->getBuildableObject();
     if (!($object instanceof PhabricatorRepositoryCommit)) {
       return;
     }
 
     // Block until all previous builds of the same build plan have
     // finished.
     $plan = $build->getBuildPlan();
 
     $log = $build->createLog($build_target, "waiting", "blockers");
     $log_start = $log->start();
 
     $blockers = $this->getBlockers($object, $plan, $build);
     if ($blockers) {
       $log->append("Blocked by: ".implode(",", $blockers)."\n");
     }
     $log->finalize($log_start);
 
     if ($blockers) {
       throw new PhabricatorWorkerYieldException(15);
     }
   }
 
   private function getBlockers(
     PhabricatorRepositoryCommit $commit,
     HarbormasterBuildPlan $plan,
     HarbormasterBuild $source) {
 
     $call = new ConduitCall(
       'diffusion.commitparentsquery',
       array(
         'commit'   => $commit->getCommitIdentifier(),
         'callsign' => $commit->getRepository()->getCallsign()
       ));
     $call->setUser(PhabricatorUser::getOmnipotentUser());
     $parents = $call->execute();
 
     $parents = id(new DiffusionCommitQuery())
       ->setViewer(PhabricatorUser::getOmnipotentUser())
       ->withRepository($commit->getRepository())
       ->withIdentifiers($parents)
       ->execute();
 
     $blockers = array();
 
     $build_objects = array();
     foreach ($parents as $parent) {
       if (!$parent->isImported()) {
         $blockers[] = pht('Commit %s', $parent->getCommitIdentifier());
       } else {
         $build_objects[] = $parent->getPHID();
       }
     }
 
-    $buildables = id(new HarbormasterBuildableQuery())
-      ->setViewer(PhabricatorUser::getOmnipotentUser())
-      ->withBuildablePHIDs($build_objects)
-      ->withManualBuildables(false)
-      ->execute();
-    $buildable_phids = mpull($buildables, 'getPHID');
-
-    if (!$buildable_phids) {
-      return array();
-    }
-
-    $builds = id(new HarbormasterBuildQuery())
-      ->setViewer(PhabricatorUser::getOmnipotentUser())
-      ->withBuildablePHIDs($buildable_phids)
-      ->withBuildPlanPHIDs(array($plan->getPHID()))
-      ->execute();
-
-    foreach ($builds as $build) {
-      if (!$build->isComplete()) {
-        $blockers[] = pht('Build %d', $build->getID());
+    if ($build_objects) {
+      $buildables = id(new HarbormasterBuildableQuery())
+        ->setViewer(PhabricatorUser::getOmnipotentUser())
+        ->withBuildablePHIDs($build_objects)
+        ->withManualBuildables(false)
+        ->execute();
+      $buildable_phids = mpull($buildables, 'getPHID');
+
+      if ($buildable_phids) {
+        $builds = id(new HarbormasterBuildQuery())
+          ->setViewer(PhabricatorUser::getOmnipotentUser())
+          ->withBuildablePHIDs($buildable_phids)
+          ->withBuildPlanPHIDs(array($plan->getPHID()))
+          ->execute();
+
+        foreach ($builds as $build) {
+          if (!$build->isComplete()) {
+            $blockers[] = pht('Build %d', $build->getID());
+          }
+        }
       }
     }
 
     return $blockers;
   }
 
 }