diff --git a/src/applications/notification/controller/PhabricatorNotificationClearController.php b/src/applications/notification/controller/PhabricatorNotificationClearController.php
--- a/src/applications/notification/controller/PhabricatorNotificationClearController.php
+++ b/src/applications/notification/controller/PhabricatorNotificationClearController.php
@@ -5,6 +5,7 @@
 
   public function processRequest() {
     $request = $this->getRequest();
+    $chrono_key = $request->getInt('chronoKey');
     $user = $request->getUser();
 
     if ($request->isDialogFormPost()) {
@@ -12,10 +13,11 @@
 
       queryfx(
         $table->establishConnection('w'),
-        'UPDATE %T SET hasViewed = 1 WHERE
-          userPHID = %s AND hasViewed = 0',
+        'UPDATE %T SET hasViewed = 1 '.
+        'WHERE userPHID = %s AND hasViewed = 0 and chronologicalKey <= %d',
         $table->getTableName(),
-        $user->getPHID());
+        $user->getPHID(),
+        $chrono_key);
 
       return id(new AphrontReloadResponse())
         ->setURI('/notification/');
@@ -23,23 +25,31 @@
 
     $dialog = new AphrontDialogView();
     $dialog->setUser($user);
-    $dialog->setTitle('Really mark all notifications as read?');
-
-    $is_serious = PhabricatorEnv::getEnvConfig('phabricator.serious-business');
-    if ($is_serious) {
-      $dialog->appendChild(
-        pht(
-          'All unread notifications will be marked as read. You can not '.
-          'undo this action.'));
+    $dialog->addCancelButton('/notification/');
+    if ($chrono_key) {
+      $dialog->setTitle('Really mark all notifications as read?');
+      $dialog->addHiddenInput('chronoKey', $chrono_key);
+
+      $is_serious =
+        PhabricatorEnv::getEnvConfig('phabricator.serious-business');
+      if ($is_serious) {
+        $dialog->appendChild(
+          pht(
+            'All unread notifications will be marked as read. You can not '.
+            'undo this action.'));
+      } else {
+        $dialog->appendChild(
+          pht(
+            "You can't ignore your problems forever, you know."));
+      }
+
+      $dialog->addSubmitButton(pht('Mark All Read'));
     } else {
-      $dialog->appendChild(
-        pht(
-          "You can't ignore your problems forever, you know."));
+      $dialog->setTitle('No notifications to mark as read.');
+      $dialog->appendChild(pht(
+        'You have no unread notifications.'));
     }
 
-    $dialog->addCancelButton('/notification/');
-    $dialog->addSubmitButton(pht('Mark All Read'));
-
     return id(new AphrontDialogResponse())->setDialog($dialog);
   }
 }
diff --git a/src/applications/notification/controller/PhabricatorNotificationListController.php b/src/applications/notification/controller/PhabricatorNotificationListController.php
--- a/src/applications/notification/controller/PhabricatorNotificationListController.php
+++ b/src/applications/notification/controller/PhabricatorNotificationListController.php
@@ -39,33 +39,37 @@
         break;
     }
 
-    $notifications = $query->executeWithOffsetPager($pager);
+    $image = id(new PHUIIconView())
+      ->setIconFont('fa-eye-slash');
+    $button = id(new PHUIButtonView())
+      ->setTag('a')
+      ->addSigil('workflow')
+      ->setColor(PHUIButtonView::SIMPLE)
+      ->setIcon($image)
+      ->setText(pht('Mark All Read'));
 
+    $notifications = $query->executeWithOffsetPager($pager);
+    $clear_uri = id(new PhutilURI('/notification/clear/'));
     if ($notifications) {
       $builder = new PhabricatorNotificationBuilder($notifications);
       $builder->setUser($user);
       $view = $builder->buildView()->render();
+      $clear_uri->setQueryParam(
+        'chronoKey',
+        head($notifications)->getChronologicalKey());
     } else {
       $view = phutil_tag_div(
         'phabricator-notification no-notifications',
         $no_data);
+      $button->setDisabled(true);
     }
+    $button->setHref((string) $clear_uri);
 
     $view = id(new PHUIBoxView())
       ->addPadding(PHUI::PADDING_MEDIUM)
       ->addClass('phabricator-notification-list')
       ->appendChild($view);
 
-    $image = id(new PHUIIconView())
-        ->setIconFont('fa-eye-slash');
-    $button = id(new PHUIButtonView())
-        ->setTag('a')
-        ->setColor(PHUIButtonView::SIMPLE)
-        ->setHref('/notification/clear/')
-        ->addSigil('workflow')
-        ->setIcon($image)
-        ->setText(pht('Mark All Read'));
-
     $notif_header = id(new PHUIHeaderView())
       ->setHeader($header)
       ->addActionLink($button);
diff --git a/src/applications/notification/controller/PhabricatorNotificationPanelController.php b/src/applications/notification/controller/PhabricatorNotificationPanelController.php
--- a/src/applications/notification/controller/PhabricatorNotificationPanelController.php
+++ b/src/applications/notification/controller/PhabricatorNotificationPanelController.php
@@ -15,15 +15,29 @@
 
     $stories = $query->execute();
 
+    $clear_ui_class = 'phabricator-notification-clear-all';
+    $clear_uri = id(new PhutilURI('/notification/clear/'));
     if ($stories) {
       $builder = new PhabricatorNotificationBuilder($stories);
       $notifications_view = $builder->buildView();
       $content = $notifications_view->render();
+      $clear_uri->setQueryParam(
+        'chronoKey',
+        head($stories)->getChronologicalKey());
     } else {
       $content = phutil_tag_div(
         'phabricator-notification no-notifications',
         pht('You have no notifications.'));
+      $clear_ui_class .= ' disabled';
     }
+    $clear_ui = javelin_tag(
+      'a',
+      array(
+        'sigil' => 'workflow',
+        'href' => (string) $clear_uri,
+        'class' => $clear_ui_class,
+      ),
+      pht('Mark All Read'));
 
     $notifications_link = phutil_tag(
       'a',
@@ -50,14 +64,7 @@
       '<div class="phabricator-notification-view-all">%s %s %s</div>',
       $header,
       $content,
-      javelin_tag(
-        'a',
-        array(
-          'sigil' => 'workflow',
-          'href' => '/notification/clear/',
-          'class' => 'phabricator-notification-clear-all'
-        ),
-        pht('Mark All Read')),
+      $clear_ui,
       " \xC2\xB7 ",
       phutil_tag(
         'a',