diff --git a/src/applications/diffusion/controller/DiffusionServeController.php b/src/applications/diffusion/controller/DiffusionServeController.php
--- a/src/applications/diffusion/controller/DiffusionServeController.php
+++ b/src/applications/diffusion/controller/DiffusionServeController.php
@@ -262,17 +262,23 @@
         case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
           $result = new PhabricatorVCSResponse(
             500,
-            pht('This is not a Git repository.'));
+            pht(
+              'This repository ("%s") is not a Git repository.',
+              $repository->getDisplayName()));
           break;
         case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
           $result = new PhabricatorVCSResponse(
             500,
-            pht('This is not a Mercurial repository.'));
+            pht(
+              'This repository ("%s") is not a Mercurial repository.',
+              $repository->getDisplayName()));
           break;
         case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
           $result = new PhabricatorVCSResponse(
             500,
-            pht('This is not a Subversion repository.'));
+            pht(
+              'This repository ("%s") is not a Subversion repository.',
+              $repository->getDisplayName()));
           break;
         default:
           $result = new PhabricatorVCSResponse(
@@ -480,7 +486,9 @@
   private function getRequestDirectoryPath(PhabricatorRepository $repository) {
     $request = $this->getRequest();
     $request_path = $request->getRequestURI()->getPath();
-    $base_path = preg_replace('@^/diffusion/[A-Z]+@', '', $request_path);
+
+    $info = PhabricatorRepository::parseRepositoryServicePath($request_path);
+    $base_path = $info['path'];
 
     // For Git repositories, strip an optional directory component if it
     // isn't the name of a known Git resource. This allows users to clone
diff --git a/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php b/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
--- a/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
+++ b/src/applications/diffusion/ssh/DiffusionSSHWorkflow.php
@@ -6,6 +6,7 @@
   private $repository;
   private $hasWriteAccess;
   private $proxyURI;
+  private $baseRequestPath;
 
   public function getRepository() {
     if (!$this->repository) {
@@ -45,6 +46,10 @@
   abstract protected function identifyRepository();
   abstract protected function executeRepositoryOperations();
 
+  protected function getBaseRequestPath() {
+    return $this->baseRequestPath;
+  }
+
   protected function writeError($message) {
     $this->getErrorChannel()->write($message);
     return $this;
@@ -149,25 +154,29 @@
   protected function loadRepositoryWithPath($path) {
     $viewer = $this->getUser();
 
-    $regex = '@^/?diffusion/(?P<callsign>[A-Z]+)(?:/|\z)@';
-    $matches = null;
-    if (!preg_match($regex, $path, $matches)) {
+    $info = PhabricatorRepository::parseRepositoryServicePath($path);
+    if ($info === null) {
       throw new Exception(
         pht(
-          'Unrecognized repository path "%s". Expected a path like "%s".',
+          'Unrecognized repository path "%s". Expected a path like "%s" '.
+          'or "%s".',
           $path,
-          '/diffusion/X/'));
+          '/diffusion/X/',
+          '/diffusion/123/'));
     }
 
-    $callsign = $matches[1];
+    $identifier = $info['identifier'];
+    $base = $info['base'];
+
+    $this->baseRequestPath = $base;
+
     $repository = id(new PhabricatorRepositoryQuery())
       ->setViewer($viewer)
-      ->withCallsigns(array($callsign))
+      ->withIdentifiers(array($identifier))
       ->executeOne();
-
     if (!$repository) {
       throw new Exception(
-        pht('No repository "%s" exists!', $callsign));
+        pht('No repository "%s" exists!', $identifier));
     }
 
     switch ($repository->getServeOverSSH()) {
@@ -179,7 +188,9 @@
       case PhabricatorRepository::SERVE_OFF:
       default:
         throw new Exception(
-          pht('This repository is not available over SSH.'));
+          pht(
+            'This repository ("%s") is not available over SSH.',
+            $repository->getDisplayName()));
     }
 
     return $repository;
diff --git a/src/applications/diffusion/ssh/DiffusionSubversionServeSSHWorkflow.php b/src/applications/diffusion/ssh/DiffusionSubversionServeSSHWorkflow.php
--- a/src/applications/diffusion/ssh/DiffusionSubversionServeSSHWorkflow.php
+++ b/src/applications/diffusion/ssh/DiffusionSubversionServeSSHWorkflow.php
@@ -377,14 +377,12 @@
     $repository = $this->getRepository();
 
     $path = $this->getPathFromSubversionURI($uri_string);
-    $path = preg_replace(
-      '(^/diffusion/[A-Z]+)',
-      rtrim($repository->getLocalPath(), '/'),
-      $path);
+    $external_base = $this->getBaseRequestPath();
 
-    if (preg_match('(^/diffusion/[A-Z]+/\z)', $path)) {
-      $path = rtrim($path, '/');
-    }
+    // Replace "/diffusion/X" in the request with the repository local path,
+    // so "/diffusion/X/master/" becomes "/path/to/repository/X/master/".
+    $local_path = rtrim($repository->getLocalPath(), '/');
+    $path = $local_path.substr($path, strlen($external_base));
 
     // NOTE: We are intentionally NOT removing username information from the
     // URI. Subversion retains it over the course of the request and considers
@@ -398,7 +396,7 @@
     if ($this->externalBaseURI === null) {
       $pre = (string)id(clone $uri)->setPath('');
 
-      $external_path = '/diffusion/'.$repository->getCallsign();
+      $external_path = $external_base;
       $external_path = $this->normalizeSVNPath($external_path);
       $this->externalBaseURI = $pre.$external_path;
 
diff --git a/src/applications/repository/storage/PhabricatorRepository.php b/src/applications/repository/storage/PhabricatorRepository.php
--- a/src/applications/repository/storage/PhabricatorRepository.php
+++ b/src/applications/repository/storage/PhabricatorRepository.php
@@ -687,6 +687,41 @@
     return "/r{$callsign}{$identifier}";
   }
 
+  public static function parseRepositoryServicePath($request_path) {
+    // NOTE: In Mercurial over SSH, the path will begin without a leading "/",
+    // so we're matching it optionally.
+
+    $patterns = array(
+      '(^'.
+        '(?P<base>/?diffusion/(?P<identifier>[A-Z]+|[0-9]\d*))'.
+        '(?P<path>(?:/.*)?)'.
+      '\z)',
+    );
+
+    $identifier = null;
+    foreach ($patterns as $pattern) {
+      $matches = null;
+      if (!preg_match($pattern, $request_path, $matches)) {
+        continue;
+      }
+
+      $identifier = $matches['identifier'];
+      $base = $matches['base'];
+      $path = $matches['path'];
+      break;
+    }
+
+    if ($identifier === null) {
+      return null;
+    }
+
+    return array(
+      'identifier' => $identifier,
+      'base' => $base,
+      'path' => $path,
+    );
+  }
+
   public function getCanonicalPath($request_path) {
     $standard_pattern =
       '(^'.