diff --git a/src/applications/differential/conduit/ConduitAPI_differential_creatediff_Method.php b/src/applications/differential/conduit/ConduitAPI_differential_creatediff_Method.php
index d2f4b9a499..68a6284929 100644
--- a/src/applications/differential/conduit/ConduitAPI_differential_creatediff_Method.php
+++ b/src/applications/differential/conduit/ConduitAPI_differential_creatediff_Method.php
@@ -1,153 +1,157 @@
 <?php
 
 /**
  * @group conduit
  */
 final class ConduitAPI_differential_creatediff_Method extends ConduitAPIMethod {
 
   public function getMethodDescription() {
     return "Create a new Differential diff.";
   }
 
   public function defineParamTypes() {
     return array(
       'changes'                   => 'required list<dict>',
       'sourceMachine'             => 'required string',
       'sourcePath'                => 'required string',
       'branch'                    => 'required string',
       'bookmark'                  => 'optional string',
       'sourceControlSystem'       => 'required enum<svn, git>',
       'sourceControlPath'         => 'required string',
       'sourceControlBaseRevision' => 'required string',
       'parentRevisionID'          => 'optional revisionid',
       'creationMethod'            => 'optional string',
       'authorPHID'                => 'optional phid',
       'arcanistProject'           => 'optional string',
       'repositoryUUID'            => 'optional string',
       'lintStatus'                =>
         'required enum<none, skip, okay, warn, fail, postponed>',
       'unitStatus'                =>
         'required enum<none, skip, okay, warn, fail, postponed>',
     );
   }
 
   public function defineReturnType() {
     return 'nonempty dict';
   }
 
   public function defineErrorTypes() {
     return array(
     );
   }
 
   protected function execute(ConduitAPIRequest $request) {
     $change_data = $request->getValue('changes');
 
     $changes = array();
     foreach ($change_data as $dict) {
       $changes[] = ArcanistDiffChange::newFromDictionary($dict);
     }
 
     $diff = DifferentialDiff::newFromRawChanges($changes);
     $diff->setSourcePath($request->getValue('sourcePath'));
     $diff->setSourceMachine($request->getValue('sourceMachine'));
 
     $diff->setBranch($request->getValue('branch'));
     $diff->setCreationMethod($request->getValue('creationMethod'));
     $diff->setAuthorPHID($request->getValue('authorPHID'));
     $diff->setBookmark($request->getValue('bookmark'));
 
     $parent_id = $request->getValue('parentRevisionID');
     if ($parent_id) {
+      // NOTE: If the viewer can't see the parent revision, just don't set
+      // a parent revision ID. This isn't used for anything meaningful.
+      // TODO: Can we delete this entirely?
       $parent_rev = id(new DifferentialRevisionQuery())
         ->setViewer($request->getUser())
         ->withIDs(array($parent_id))
-        ->executeOne();
+        ->execute();
       if ($parent_rev) {
+        $parent_rev = head($parent_rev);
         if ($parent_rev->getStatus() !=
             ArcanistDifferentialRevisionStatus::CLOSED) {
           $diff->setParentRevisionID($parent_id);
         }
       }
     }
 
     $system = $request->getValue('sourceControlSystem');
     $diff->setSourceControlSystem($system);
     $diff->setSourceControlPath($request->getValue('sourceControlPath'));
     $diff->setSourceControlBaseRevision(
       $request->getValue('sourceControlBaseRevision'));
 
     $project_name = $request->getValue('arcanistProject');
     $project_phid = null;
     if ($project_name) {
       $arcanist_project = id(new PhabricatorRepositoryArcanistProject())
         ->loadOneWhere(
           'name = %s',
           $project_name);
       if (!$arcanist_project) {
         $arcanist_project = new PhabricatorRepositoryArcanistProject();
         $arcanist_project->setName($project_name);
         $arcanist_project->save();
       }
       $project_phid = $arcanist_project->getPHID();
     }
 
     $diff->setArcanistProjectPHID($project_phid);
     $diff->setRepositoryUUID($request->getValue('repositoryUUID'));
 
     switch ($request->getValue('lintStatus')) {
       case 'skip':
         $diff->setLintStatus(DifferentialLintStatus::LINT_SKIP);
         break;
       case 'okay':
         $diff->setLintStatus(DifferentialLintStatus::LINT_OKAY);
         break;
       case 'warn':
         $diff->setLintStatus(DifferentialLintStatus::LINT_WARN);
         break;
       case 'fail':
         $diff->setLintStatus(DifferentialLintStatus::LINT_FAIL);
         break;
       case 'postponed':
         $diff->setLintStatus(DifferentialLintStatus::LINT_POSTPONED);
         break;
       case 'none':
       default:
         $diff->setLintStatus(DifferentialLintStatus::LINT_NONE);
         break;
     }
 
     switch ($request->getValue('unitStatus')) {
       case 'skip':
         $diff->setUnitStatus(DifferentialUnitStatus::UNIT_SKIP);
         break;
       case 'okay':
         $diff->setUnitStatus(DifferentialUnitStatus::UNIT_OKAY);
         break;
       case 'warn':
         $diff->setUnitStatus(DifferentialUnitStatus::UNIT_WARN);
         break;
       case 'fail':
         $diff->setUnitStatus(DifferentialUnitStatus::UNIT_FAIL);
         break;
       case 'postponed':
         $diff->setUnitStatus(DifferentialUnitStatus::UNIT_POSTPONED);
         break;
       case 'none':
       default:
         $diff->setUnitStatus(DifferentialUnitStatus::UNIT_NONE);
         break;
     }
 
     $diff->save();
 
     $path = '/differential/diff/'.$diff->getID().'/';
     $uri = PhabricatorEnv::getURI($path);
 
     return array(
       'diffid' => $diff->getID(),
       'uri'    => $uri,
     );
   }
 
 }