diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index d7f399560d..6f8afa6705 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -906,6 +906,7 @@ phutil_register_library_map(array(
     'PhabricatorProjectCreateController' => 'applications/project/controller/PhabricatorProjectCreateController.php',
     'PhabricatorProjectDAO' => 'applications/project/storage/PhabricatorProjectDAO.php',
     'PhabricatorProjectEditor' => 'applications/project/editor/PhabricatorProjectEditor.php',
+    'PhabricatorProjectEditorTestCase' => 'applications/project/editor/__tests__/PhabricatorProjectEditorTestCase.php',
     'PhabricatorProjectListController' => 'applications/project/controller/PhabricatorProjectListController.php',
     'PhabricatorProjectMembersEditController' => 'applications/project/controller/PhabricatorProjectMembersEditController.php',
     'PhabricatorProjectNameCollisionException' => 'applications/project/exception/PhabricatorProjectNameCollisionException.php',
@@ -1986,6 +1987,7 @@ phutil_register_library_map(array(
     'PhabricatorProjectController' => 'PhabricatorController',
     'PhabricatorProjectCreateController' => 'PhabricatorProjectController',
     'PhabricatorProjectDAO' => 'PhabricatorLiskDAO',
+    'PhabricatorProjectEditorTestCase' => 'PhabricatorTestCase',
     'PhabricatorProjectListController' => 'PhabricatorProjectController',
     'PhabricatorProjectMembersEditController' => 'PhabricatorProjectController',
     'PhabricatorProjectNameCollisionException' => 'Exception',
diff --git a/src/applications/project/controller/PhabricatorProjectUpdateController.php b/src/applications/project/controller/PhabricatorProjectUpdateController.php
index 32adf77bc8..b12bcc8fa7 100644
--- a/src/applications/project/controller/PhabricatorProjectUpdateController.php
+++ b/src/applications/project/controller/PhabricatorProjectUpdateController.php
@@ -31,7 +31,11 @@ final class PhabricatorProjectUpdateController
     $request = $this->getRequest();
     $user = $request->getUser();
 
-    $project = id(new PhabricatorProject())->load($this->id);
+    $project = id(new PhabricatorProjectQuery())
+      ->setViewer($user)
+      ->needMembers(true)
+      ->withIDs(array($this->id))
+      ->executeOne();
     if (!$project) {
       return new Aphront404Response();
     }
@@ -51,44 +55,14 @@ final class PhabricatorProjectUpdateController
     $project_uri = '/project/view/'.$project->getID().'/';
 
     if ($process_action) {
-      $xactions = array();
-
-
       switch ($this->action) {
         case 'join':
-          $member_phids = $project->loadMemberPHIDs();
-          $member_map = array_fill_keys($member_phids, true);
-          if (empty($member_map[$user->getPHID()])) {
-            $member_map[$user->getPHID()] = true;
-
-            $xaction = new PhabricatorProjectTransaction();
-            $xaction->setTransactionType(
-              PhabricatorProjectTransactionType::TYPE_MEMBERS);
-            $xaction->setNewValue(array_keys($member_map));
-            $xactions[] = $xaction;
-          }
+          PhabricatorProjectEditor::applyJoinProject($project, $user);
           break;
         case 'leave':
-          $member_phids = $project->loadMemberPHIDs();
-          $member_map = array_fill_keys($member_phids, true);
-          if (isset($member_map[$user->getPHID()])) {
-            unset($member_map[$user->getPHID()]);
-
-            $xaction = new PhabricatorProjectTransaction();
-            $xaction->setTransactionType(
-              PhabricatorProjectTransactionType::TYPE_MEMBERS);
-            $xaction->setNewValue(array_keys($member_map));
-            $xactions[] = $xaction;
-          }
+          PhabricatorProjectEditor::applyLeaveProject($project, $user);
           break;
       }
-
-      if ($xactions) {
-        $editor = new PhabricatorProjectEditor($project);
-        $editor->setUser($user);
-        $editor->applyTransactions($xactions);
-      }
-
       return id(new AphrontRedirectResponse())->setURI($project_uri);
     }
 
diff --git a/src/applications/project/editor/PhabricatorProjectEditor.php b/src/applications/project/editor/PhabricatorProjectEditor.php
index 86c39d0a98..4c8646d9c6 100644
--- a/src/applications/project/editor/PhabricatorProjectEditor.php
+++ b/src/applications/project/editor/PhabricatorProjectEditor.php
@@ -25,6 +25,51 @@ final class PhabricatorProjectEditor {
   private $addEdges = array();
   private $remEdges = array();
 
+  public static function applyJoinProject(
+    PhabricatorProject $project,
+    PhabricatorUser $user) {
+
+    $members = $project->getMemberPHIDs();
+    $members[] = $user->getPHID();
+
+    self::applyOneTransaction(
+      $project,
+      $user,
+      PhabricatorProjectTransactionType::TYPE_MEMBERS,
+      $members);
+  }
+
+  public static function applyLeaveProject(
+    PhabricatorProject $project,
+    PhabricatorUser $user) {
+
+    $members = array_fill_keys($project->getMemberPHIDs(), true);
+    unset($members[$user->getPHID()]);
+    $members = array_keys($members);
+
+    self::applyOneTransaction(
+      $project,
+      $user,
+      PhabricatorProjectTransactionType::TYPE_MEMBERS,
+      $members);
+  }
+
+  private static function applyOneTransaction(
+    PhabricatorProject $project,
+    PhabricatorUser $user,
+    $type,
+    $new_value) {
+
+    $xaction = new PhabricatorProjectTransaction();
+    $xaction->setTransactionType($type);
+    $xaction->setNewValue($new_value);
+
+    $editor = new PhabricatorProjectEditor($project);
+    $editor->setUser($user);
+    $editor->applyTransactions(array($xaction));
+  }
+
+
   public function __construct(PhabricatorProject $project) {
     $this->project = $project;
   }
diff --git a/src/applications/project/editor/__tests__/PhabricatorProjectEditorTestCase.php b/src/applications/project/editor/__tests__/PhabricatorProjectEditorTestCase.php
new file mode 100644
index 0000000000..dafedfe23b
--- /dev/null
+++ b/src/applications/project/editor/__tests__/PhabricatorProjectEditorTestCase.php
@@ -0,0 +1,138 @@
+<?php
+
+/*
+ * Copyright 2012 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+final class PhabricatorProjectEditorTestCase extends PhabricatorTestCase {
+
+  protected function getPhabricatorTestCaseConfiguration() {
+    return array(
+      self::PHABRICATOR_TESTCONFIG_BUILD_STORAGE_FIXTURES => true,
+    );
+  }
+
+  public function testJoinLeaveProject() {
+    $user = $this->createUser();
+    $user->save();
+
+    $proj = $this->createProjectWithNewAuthor();
+    $proj->save();
+
+    $proj = $this->refreshProject($proj, $user, true);
+    $this->assertEqual(
+      true,
+      (bool)$proj,
+      'Assumption that projects are default visible to any user when created.');
+
+    $this->assertEqual(
+      false,
+      $proj->isUserMember($user->getPHID()),
+      'Arbitrary user not member of project.');
+
+    // Join the project.
+    PhabricatorProjectEditor::applyJoinProject($proj, $user);
+
+    $proj = $this->refreshProject($proj, $user, true);
+    $this->assertEqual(true, (bool)$proj);
+
+    $this->assertEqual(
+      true,
+      $proj->isUserMember($user->getPHID()),
+      'Join works.');
+
+
+    // Join the project again.
+    PhabricatorProjectEditor::applyJoinProject($proj, $user);
+
+    $proj = $this->refreshProject($proj, $user, true);
+    $this->assertEqual(true, (bool)$proj);
+
+    $this->assertEqual(
+      true,
+      $proj->isUserMember($user->getPHID()),
+      'Joining an already-joined project is a no-op.');
+
+
+    // Leave the project.
+    PhabricatorProjectEditor::applyLeaveProject($proj, $user);
+
+    $proj = $this->refreshProject($proj, $user, true);
+    $this->assertEqual(true, (bool)$proj);
+
+    $this->assertEqual(
+      false,
+      $proj->isUserMember($user->getPHID()),
+      'Leave works.');
+
+
+    // Leave the project again.
+    PhabricatorProjectEditor::applyLeaveProject($proj, $user);
+
+    $proj = $this->refreshProject($proj, $user, true);
+    $this->assertEqual(true, (bool)$proj);
+
+    $this->assertEqual(
+      false,
+      $proj->isUserMember($user->getPHID()),
+      'Leaving an already-left project is a no-op.');
+  }
+
+  private function refreshProject(
+    PhabricatorProject $project,
+    PhabricatorUser $viewer,
+    $need_members = false) {
+
+    $results = id(new PhabricatorProjectQuery())
+      ->setViewer($viewer)
+      ->needMembers($need_members)
+      ->withIDs(array($project->getID()))
+      ->execute();
+
+    if ($results) {
+      return head($results);
+    } else {
+      return null;
+    }
+  }
+
+  private function createProject() {
+    $project = new PhabricatorProject();
+    $project->setName('Test Project '.mt_rand());
+
+    return $project;
+  }
+
+  private function createProjectWithNewAuthor() {
+    $author = $this->createUser();
+    $author->save();
+
+    $project = $this->createProject();
+    $project->setAuthorPHID($author->getPHID());
+
+    return $project;
+  }
+
+  private function createUser() {
+    $rand = mt_rand();
+
+    $user = new PhabricatorUser();
+    $user->setUsername('unittestuser'.$rand);
+    $user->setRealName('Unit Test User '.$rand);
+
+    return $user;
+  }
+
+}