diff --git a/src/applications/phriction/controller/PhrictionEditController.php b/src/applications/phriction/controller/PhrictionEditController.php
index e9df079fdb..7750aaab4b 100644
--- a/src/applications/phriction/controller/PhrictionEditController.php
+++ b/src/applications/phriction/controller/PhrictionEditController.php
@@ -1,258 +1,289 @@
 <?php
 
 /**
  * @group phriction
  */
 final class PhrictionEditController
   extends PhrictionController {
 
   private $id;
 
   public function willProcessRequest(array $data) {
     $this->id = idx($data, 'id');
   }
 
   public function processRequest() {
 
     $request = $this->getRequest();
     $user = $request->getUser();
 
     if ($this->id) {
       $document = id(new PhrictionDocument())->load($this->id);
       if (!$document) {
         return new Aphront404Response();
       }
 
       $revert = $request->getInt('revert');
       if ($revert) {
         $content = id(new PhrictionContent())->loadOneWhere(
           'documentID = %d AND version = %d',
           $document->getID(),
           $revert);
         if (!$content) {
           return new Aphront404Response();
         }
       } else {
         $content = id(new PhrictionContent())->load($document->getContentID());
       }
 
     } else {
       $slug = $request->getStr('slug');
       $slug = PhabricatorSlug::normalize($slug);
       if (!$slug) {
         return new Aphront404Response();
       }
 
       $document = id(new PhrictionDocument())->loadOneWhere(
         'slug = %s',
         $slug);
 
       if ($document) {
         $content = id(new PhrictionContent())->load($document->getContentID());
       } else {
         if (PhrictionDocument::isProjectSlug($slug)) {
           $project = id(new PhabricatorProjectQuery())
             ->setViewer($user)
             ->withPhrictionSlugs(array(
               PhrictionDocument::getProjectSlugIdentifier($slug)))
             ->executeOne();
           if (!$project) {
             return new Aphront404Response();
           }
         }
         $document = new PhrictionDocument();
         $document->setSlug($slug);
 
         $content  = new PhrictionContent();
         $content->setSlug($slug);
 
         $default_title = PhabricatorSlug::getDefaultTitle($slug);
         $content->setTitle($default_title);
       }
     }
 
     if ($request->getBool('nodraft')) {
       $draft = null;
       $draft_key = null;
     } else {
       if ($document->getPHID()) {
         $draft_key = $document->getPHID().':'.$content->getVersion();
       } else {
         $draft_key = 'phriction:'.$content->getSlug();
       }
       $draft = id(new PhabricatorDraft())->loadOneWhere(
         'authorPHID = %s AND draftKey = %s',
         $user->getPHID(),
         $draft_key);
     }
 
     require_celerity_resource('phriction-document-css');
 
     $e_title = true;
     $notes = null;
     $errors = array();
 
     if ($request->isFormPost()) {
+
+      $overwrite = $request->getBool('overwrite');
+      if (!$overwrite) {
+        $edit_version = $request->getStr('contentVersion');
+        $current_version = $content->getVersion();
+        if ($edit_version != $current_version) {
+          $dialog = $this->newDialog()
+            ->setTitle(pht('Edit Conflict!'))
+            ->appendParagraph(
+              pht(
+                'Another user made changes to this document after you began '.
+                'editing it. Do you want to overwrite their changes?'))
+            ->appendParagraph(
+              pht(
+                'If you choose to overwrite their changes, you should review '.
+                'the document edit history to see what you overwrote, and '.
+                'then make another edit to merge the changes if necessary.'))
+            ->addSubmitButton(pht('Overwrite Changes'))
+            ->addCancelButton($request->getRequestURI());
+
+          $dialog->addHiddenInput('overwrite', 'true');
+          foreach ($request->getPassthroughRequestData() as $key => $value) {
+            $dialog->addHiddenInput($key, $value);
+          }
+
+          return $dialog;
+        }
+      }
+
+
       $title = $request->getStr('title');
       $notes = $request->getStr('description');
 
       if (!strlen($title)) {
         $e_title = pht('Required');
         $errors[] = pht('Document title is required.');
       } else {
         $e_title = null;
       }
 
       if ($document->getID()) {
         if ($content->getTitle() == $title &&
             $content->getContent() == $request->getStr('content')) {
 
           $dialog = new AphrontDialogView();
           $dialog->setUser($user);
           $dialog->setTitle(pht('No Edits'));
           $dialog->appendChild(phutil_tag('p', array(), pht(
             'You did not make any changes to the document.')));
           $dialog->addCancelButton($request->getRequestURI());
 
           return id(new AphrontDialogResponse())->setDialog($dialog);
         }
       } else if (!strlen($request->getStr('content'))) {
 
         // We trigger this only for new pages. For existing pages, deleting
         // all the content counts as deleting the page.
 
         $dialog = new AphrontDialogView();
         $dialog->setUser($user);
         $dialog->setTitle(pht('Empty Page'));
         $dialog->appendChild(phutil_tag('p', array(), pht(
           'You can not create an empty document.')));
         $dialog->addCancelButton($request->getRequestURI());
 
         return id(new AphrontDialogResponse())->setDialog($dialog);
       }
 
       if (!count($errors)) {
         $editor = id(PhrictionDocumentEditor::newForSlug($document->getSlug()))
           ->setActor($user)
           ->setTitle($title)
           ->setContent($request->getStr('content'))
           ->setDescription($notes);
 
         $editor->save();
 
         if ($draft) {
           $draft->delete();
         }
 
         $uri = PhrictionDocument::getSlugURI($document->getSlug());
         return id(new AphrontRedirectResponse())->setURI($uri);
       }
     }
 
     if ($document->getID()) {
       $panel_header = pht('Edit Phriction Document');
       $submit_button = pht('Save Changes');
     } else {
       $panel_header = pht('Create New Phriction Document');
       $submit_button = pht('Create Document');
     }
 
     $uri = $document->getSlug();
     $uri = PhrictionDocument::getSlugURI($uri);
     $uri = PhabricatorEnv::getProductionURI($uri);
 
     $cancel_uri = PhrictionDocument::getSlugURI($document->getSlug());
 
     if ($draft &&
         strlen($draft->getDraft()) &&
         ($draft->getDraft() != $content->getContent())) {
       $content_text = $draft->getDraft();
 
       $discard = phutil_tag(
         'a',
         array(
           'href' => $request->getRequestURI()->alter('nodraft', true),
         ),
         pht('discard this draft'));
 
       $draft_note = new AphrontErrorView();
       $draft_note->setSeverity(AphrontErrorView::SEVERITY_NOTICE);
       $draft_note->setTitle('Recovered Draft');
       $draft_note->appendChild(hsprintf(
         '<p>Showing a saved draft of your edits, you can %s.</p>',
         $discard));
     } else {
       $content_text = $content->getContent();
       $draft_note = null;
     }
 
     $form = id(new AphrontFormView())
       ->setUser($user)
       ->setWorkflow(true)
       ->setAction($request->getRequestURI()->getPath())
       ->addHiddenInput('slug', $document->getSlug())
       ->addHiddenInput('nodraft', $request->getBool('nodraft'))
+      ->addHiddenInput('contentVersion', $content->getVersion())
       ->appendChild(
         id(new AphrontFormTextControl())
           ->setLabel(pht('Title'))
           ->setValue($content->getTitle())
           ->setError($e_title)
           ->setName('title'))
       ->appendChild(
         id(new AphrontFormStaticControl())
           ->setLabel(pht('URI'))
           ->setValue($uri))
       ->appendChild(
         id(new PhabricatorRemarkupControl())
           ->setLabel(pht('Content'))
           ->setValue($content_text)
           ->setHeight(AphrontFormTextAreaControl::HEIGHT_VERY_TALL)
           ->setName('content')
           ->setID('document-textarea')
           ->setUser($user))
       ->appendChild(
         id(new AphrontFormTextControl())
           ->setLabel(pht('Edit Notes'))
           ->setValue($notes)
           ->setError(null)
           ->setName('description'))
       ->appendChild(
         id(new AphrontFormSubmitControl())
           ->addCancelButton($cancel_uri)
           ->setValue($submit_button));
 
     $form_box = id(new PHUIObjectBoxView())
       ->setHeaderText(pht('Edit Document'))
       ->setFormErrors($errors)
       ->setForm($form);
 
     $preview = id(new PHUIRemarkupPreviewPanel())
       ->setHeader(pht('Document Preview'))
       ->setPreviewURI('/phriction/preview/')
       ->setControlID('document-textarea')
       ->setSkin('document');
 
     $crumbs = $this->buildApplicationCrumbs();
     if ($document->getID()) {
       $crumbs->addTextCrumb(
         $content->getTitle(),
         PhrictionDocument::getSlugURI($document->getSlug()));
       $crumbs->addTextCrumb(pht('Edit'));
     } else {
       $crumbs->addTextCrumb(pht('Create'));
     }
 
     return $this->buildApplicationPage(
       array(
         $crumbs,
         $draft_note,
         $form_box,
         $preview,
       ),
       array(
         'title'   => pht('Edit Document'),
         'device'  => true,
       ));
   }
 
 }