diff --git a/src/applications/diffusion/controller/DiffusionCommitController.php b/src/applications/diffusion/controller/DiffusionCommitController.php
--- a/src/applications/diffusion/controller/DiffusionCommitController.php
+++ b/src/applications/diffusion/controller/DiffusionCommitController.php
@@ -7,6 +7,12 @@
   private $auditAuthorityPHIDs;
   private $highlightedAudits;
 
+  private $commitParents;
+  private $commitRefs;
+  private $commitMerges;
+  private $commitErrors;
+  private $commitExists;
+
   public function shouldAllowPublic() {
     return true;
   }
@@ -17,6 +23,7 @@
 
   protected function processDiffusionRequest(AphrontRequest $request) {
     $user = $request->getUser();
+
     // This controller doesn't use blob/path stuff, just pass the dictionary
     // in directly instead of using the AphrontRequest parsing mechanism.
     $data = $request->getURIMap();
@@ -45,10 +52,7 @@
     ));
 
     if (!$commit) {
-      $exists = $this->callConduitWithDiffusionRequest(
-        'diffusion.existsquery',
-        array('commit' => $drequest->getCommit()));
-      if (!$exists) {
+      if (!$this->getCommitExists()) {
         return new Aphront404Response();
       }
 
@@ -95,18 +99,6 @@
 
       require_celerity_resource('phabricator-remarkup-css');
 
-      $parents = $this->callConduitWithDiffusionRequest(
-        'diffusion.commitparentsquery',
-        array('commit' => $drequest->getCommit()));
-
-      if ($parents) {
-        $parents = id(new DiffusionCommitQuery())
-          ->setViewer($user)
-          ->withRepository($repository)
-          ->withIdentifiers($parents)
-          ->execute();
-      }
-
       $headsup_view = id(new PHUIHeaderView())
         ->setHeader(nonempty($commit->getSummary(), pht('Commit Detail')));
 
@@ -115,7 +107,6 @@
       $commit_properties = $this->loadCommitProperties(
         $commit,
         $commit_data,
-        $parents,
         $audit_requests);
       $property_list = id(new PHUIPropertyListView())
         ->setHasKeyboardShortcuts(true)
@@ -148,8 +139,10 @@
           $message));
 
       $headsup_view->setTall(true);
+
       $object_box = id(new PHUIObjectBoxView())
         ->setHeader($headsup_view)
+        ->setFormErrors($this->getCommitErrors())
         ->addPropertyList($property_list)
         ->addPropertyList($detail_list);
 
@@ -216,6 +209,10 @@
           'This commit is enormous, and affects more than %d files. '.
           'Changes are not shown.',
           $hard_limit));
+    } else if (!$this->getCommitExists()) {
+      $content[] = $this->renderStatusMessage(
+        pht('Commit No Longer Exists'),
+        pht('This commit no longer exists in the repository.'));
     } else {
       $show_changesets = true;
 
@@ -382,10 +379,8 @@
   private function loadCommitProperties(
     PhabricatorRepositoryCommit $commit,
     PhabricatorRepositoryCommitData $data,
-    array $parents,
     array $audit_requests) {
 
-    assert_instances_of($parents, 'PhabricatorRepositoryCommit');
     $viewer = $this->getRequest()->getUser();
     $commit_phid = $commit->getPHID();
     $drequest = $this->getDiffusionRequest();
@@ -423,11 +418,6 @@
     if ($data->getCommitDetail('committerPHID')) {
       $phids[] = $data->getCommitDetail('committerPHID');
     }
-    if ($parents) {
-      foreach ($parents as $parent) {
-        $phids[] = $parent->getPHID();
-      }
-    }
 
     // NOTE: We should never normally have more than a single push log, but
     // it can occur naturally if a commit is pushed, then the branch it was
@@ -564,39 +554,47 @@
       $props['Differential Revision'] = $handles[$revision_phid]->renderLink();
     }
 
+    $parents = $this->getCommitParents();
     if ($parents) {
-      $parent_links = array();
-      foreach ($parents as $parent) {
-        $parent_links[] = $handles[$parent->getPHID()]->renderLink();
-      }
-      $props['Parents'] = phutil_implode_html(" \xC2\xB7 ", $parent_links);
+      $props['Parents'] = $viewer->renderHandleList(mpull($parents, 'getPHID'));
     }
 
-    $props['Branches'] = phutil_tag(
-      'span',
-      array(
-        'id' => 'commit-branches',
-      ),
-      pht('Unknown'));
-    $props['Tags'] = phutil_tag(
-      'span',
-      array(
-        'id' => 'commit-tags',
-      ),
-      pht('Unknown'));
+    if ($this->getCommitExists()) {
+      $props['Branches'] = phutil_tag(
+        'span',
+        array(
+          'id' => 'commit-branches',
+        ),
+        pht('Unknown'));
+      $props['Tags'] = phutil_tag(
+        'span',
+        array(
+          'id' => 'commit-tags',
+        ),
+        pht('Unknown'));
 
-    $callsign = $repository->getCallsign();
-    $root = '/diffusion/'.$callsign.'/commit/'.$commit->getCommitIdentifier();
-    Javelin::initBehavior(
-      'diffusion-commit-branches',
-      array(
-        $root.'/branches/' => 'commit-branches',
-        $root.'/tags/' => 'commit-tags',
-      ));
+      $callsign = $repository->getCallsign();
+      $root = '/diffusion/'.$callsign.'/commit/'.$commit->getCommitIdentifier();
+      Javelin::initBehavior(
+        'diffusion-commit-branches',
+        array(
+          $root.'/branches/' => 'commit-branches',
+          $root.'/tags/' => 'commit-tags',
+        ));
+    }
 
-    $refs = $this->buildRefs($drequest);
+    $refs = $this->getCommitRefs();
     if ($refs) {
-      $props['References'] = $refs;
+      $ref_links = array();
+      foreach ($refs as $ref_data) {
+        $ref_links[] = phutil_tag(
+          'a',
+          array(
+            'href' => $ref_data['href'],
+          ),
+          $ref_data['ref']);
+      }
+      $props['References'] = phutil_implode_html(', ', $ref_links);
     }
 
     if ($reverts_phids) {
@@ -860,26 +858,12 @@
     $drequest = $this->getDiffusionRequest();
     $repository = $drequest->getRepository();
 
-    $vcs = $repository->getVersionControlSystem();
-    switch ($vcs) {
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
-        // These aren't supported under SVN.
-        return null;
-    }
-
-    $limit = 50;
-
-    $merges = $this->callConduitWithDiffusionRequest(
-      'diffusion.mergedcommitsquery',
-      array(
-        'commit' => $drequest->getCommit(),
-        'limit' => $limit + 1,
-      ));
-
+    $merges = $this->getCommitMerges();
     if (!$merges) {
       return null;
     }
-    $merges = DiffusionPathChange::newFromConduit($merges);
+
+    $limit = $this->getMergeDisplayLimit();
 
     $caption = null;
     if (count($merges) > $limit) {
@@ -961,27 +945,6 @@
     return $actions;
   }
 
-  private function buildRefs(DiffusionRequest $request) {
-    // this is git-only, so save a conduit round trip and just get out of
-    // here if the repository isn't git
-    $type_git = PhabricatorRepositoryType::REPOSITORY_TYPE_GIT;
-    $repository = $request->getRepository();
-    if ($repository->getVersionControlSystem() != $type_git) {
-      return null;
-    }
-
-    $results = $this->callConduitWithDiffusionRequest(
-      'diffusion.refsquery',
-      array('commit' => $request->getCommit()));
-    $ref_links = array();
-    foreach ($results as $ref_data) {
-      $ref_links[] = phutil_tag('a',
-        array('href' => $ref_data['href']),
-        $ref_data['ref']);
-    }
-    return phutil_implode_html(', ', $ref_links);
-  }
-
   private function buildRawDiffResponse(DiffusionRequest $drequest) {
     $raw_diff = $this->callConduitWithDiffusionRequest(
       'diffusion.rawdiffquery',
@@ -1137,4 +1100,140 @@
     return $toc_view;
   }
 
+  private function loadCommitState() {
+    $viewer = $this->getViewer();
+    $drequest = $this->getDiffusionRequest();
+    $repository = $drequest->getRepository();
+    $commit = $drequest->getCommit();
+
+    // TODO: We could use futures here and resolve these calls in parallel.
+
+    $exceptions = array();
+
+    try {
+      $parent_refs = $this->callConduitWithDiffusionRequest(
+        'diffusion.commitparentsquery',
+        array(
+          'commit' => $commit,
+        ));
+
+      if ($parent_refs) {
+        $parents = id(new DiffusionCommitQuery())
+          ->setViewer($viewer)
+          ->withRepository($repository)
+          ->withIdentifiers($parent_refs)
+          ->execute();
+      } else {
+        $parents = array();
+      }
+
+      $this->commitParents = $parents;
+    } catch (Exception $ex) {
+      $this->commitParents = false;
+      $exceptions[] = $ex;
+    }
+
+    $merge_limit = $this->getMergeDisplayLimit();
+
+    try {
+      $merges = $this->callConduitWithDiffusionRequest(
+        'diffusion.mergedcommitsquery',
+        array(
+          'commit' => $commit,
+          'limit' => $merge_limit + 1,
+        ));
+
+      $this->commitMerges = DiffusionPathChange::newFromConduit($merges);
+    } catch (Exception $ex) {
+      $this->commitMerges = false;
+      $exceptions[] = $ex;
+    }
+
+
+    try {
+      if ($repository->isGit()) {
+        $refs = $this->callConduitWithDiffusionRequest(
+          'diffusion.refsquery',
+          array(
+            'commit' => $commit,
+          ));
+      } else {
+        $refs = array();
+      }
+
+      $this->commitRefs = $refs;
+    } catch (Exception $ex) {
+      $this->commitRefs = false;
+      $exceptions[] = $ex;
+    }
+
+    if ($exceptions) {
+      $exists = $this->callConduitWithDiffusionRequest(
+        'diffusion.existsquery',
+        array(
+          'commit' => $commit,
+        ));
+
+      if ($exists) {
+        $this->commitExists = true;
+        foreach ($exceptions as $exception) {
+          $this->commitErrors[] = $exception->getMessage();
+        }
+      } else {
+        $this->commitExists = false;
+        $this->commitErrors[] = pht(
+          'This commit no longer exists in the repository. It may have '.
+          'been part of a branch which was deleted.');
+      }
+    } else {
+      $this->commitExists = true;
+      $this->commitErrors = array();
+    }
+  }
+
+  private function getMergeDisplayLimit() {
+    return 50;
+  }
+
+  private function getCommitExists() {
+    if ($this->commitExists === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitExists;
+  }
+
+  private function getCommitParents() {
+    if ($this->commitParents === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitParents;
+  }
+
+  private function getCommitRefs() {
+    if ($this->commitRefs === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitRefs;
+  }
+
+  private function getCommitMerges() {
+    if ($this->commitMerges === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitMerges;
+  }
+
+  private function getCommitErrors() {
+    if ($this->commitErrors === null) {
+      $this->loadCommitState();
+    }
+
+    return $this->commitErrors;
+  }
+
+
 }