diff --git a/src/applications/diffusion/application/PhabricatorDiffusionApplication.php b/src/applications/diffusion/application/PhabricatorDiffusionApplication.php
--- a/src/applications/diffusion/application/PhabricatorDiffusionApplication.php
+++ b/src/applications/diffusion/application/PhabricatorDiffusionApplication.php
@@ -69,10 +69,11 @@
         'branches/(?P<dblob>.*)' => 'DiffusionBranchTableController',
         'refs/(?P<dblob>.*)' => 'DiffusionRefTableController',
         'lint/(?P<dblob>.*)' => 'DiffusionLintController',
-        'commit/(?P<commit>[a-z0-9]+)/branches/'
-          => 'DiffusionCommitBranchesController',
-        'commit/(?P<commit>[a-z0-9]+)/tags/'
-          => 'DiffusionCommitTagsController',
+        'commit/(?P<commit>[a-z0-9]+)' => array(
+          '/?' => 'DiffusionCommitController',
+          '/branches/' => 'DiffusionCommitBranchesController',
+          '/tags/' => 'DiffusionCommitTagsController',
+        ),
         'compare/' => 'DiffusionCompareController',
         'manage/(?:(?P<panel>[^/]+)/)?'
           => 'DiffusionRepositoryManagePanelsController',
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
@@ -22,17 +22,27 @@
 
     $drequest = $this->getDiffusionRequest();
     $viewer = $request->getUser();
+    $repository = $drequest->getRepository();
+    $commit_identifier = $drequest->getCommit();
+
+    // If this page is being accessed via "/source/xyz/commit/...", redirect
+    // to the canonical URI.
+    $has_callsign = strlen($request->getURIData('repositoryCallsign'));
+    $has_id = strlen($request->getURIData('repositoryID'));
+    if (!$has_callsign && !$has_id) {
+      $canonical_uri = $repository->getCommitURI($commit_identifier);
+      return id(new AphrontRedirectResponse())
+        ->setURI($canonical_uri);
+    }
 
     if ($request->getStr('diff')) {
       return $this->buildRawDiffResponse($drequest);
     }
 
-    $repository = $drequest->getRepository();
-
     $commit = id(new DiffusionCommitQuery())
       ->setViewer($viewer)
       ->withRepository($repository)
-      ->withIdentifiers(array($drequest->getCommit()))
+      ->withIdentifiers(array($commit_identifier))
       ->needCommitData(true)
       ->needAuditRequests(true)
       ->executeOne();