diff --git a/src/applications/diffusion/query/diff/base/DiffusionDiffQuery.php b/src/applications/diffusion/query/diff/base/DiffusionDiffQuery.php
index 05708cc5ff..c29590ff78 100644
--- a/src/applications/diffusion/query/diff/base/DiffusionDiffQuery.php
+++ b/src/applications/diffusion/query/diff/base/DiffusionDiffQuery.php
@@ -1,7 +1,7 @@
 <?php
 
 /*
- * Copyright 2011 Facebook, Inc.
+ * Copyright 2012 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,44 +16,13 @@
  * limitations under the License.
  */
 
-abstract class DiffusionDiffQuery {
+abstract class DiffusionDiffQuery extends DiffusionQuery {
 
-  private $request;
   protected $renderingReference;
 
-  final private function __construct() {
-    // <private>
-  }
-
   final public static function newFromDiffusionRequest(
     DiffusionRequest $request) {
-
-    $repository = $request->getRepository();
-
-    switch ($repository->getVersionControlSystem()) {
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
-        $class = 'DiffusionGitDiffQuery';
-        break;
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
-        $class = 'DiffusionMercurialDiffQuery';
-        break;
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
-        $class = 'DiffusionSvnDiffQuery';
-        break;
-      default:
-        throw new Exception("Unsupported VCS!");
-    }
-
-    PhutilSymbolLoader::loadClass($class);
-    $query = new $class();
-
-    $query->request = $request;
-
-    return $query;
-  }
-
-  final protected function getRequest() {
-    return $this->request;
+    return parent::newQueryObject(__CLASS__, $request);
   }
 
   final public function getRenderingReference() {
@@ -64,8 +33,6 @@ abstract class DiffusionDiffQuery {
     return $this->executeQuery();
   }
 
-  abstract protected function executeQuery();
-
   protected function getEffectiveCommit() {
     $drequest = $this->getRequest();
 
diff --git a/src/applications/diffusion/query/diff/base/__init__.php b/src/applications/diffusion/query/diff/base/__init__.php
index d6ecf69496..bf1f89873f 100644
--- a/src/applications/diffusion/query/diff/base/__init__.php
+++ b/src/applications/diffusion/query/diff/base/__init__.php
@@ -6,10 +6,8 @@
 
 
 
+phutil_require_module('phabricator', 'applications/diffusion/query/base');
 phutil_require_module('phabricator', 'applications/diffusion/query/lastmodified/base');
-phutil_require_module('phabricator', 'applications/repository/constants/repositorytype');
-
-phutil_require_module('phutil', 'symbols');
 
 
 phutil_require_source('DiffusionDiffQuery.php');
diff --git a/src/applications/diffusion/query/diff/svn/DiffusionSvnDiffQuery.php b/src/applications/diffusion/query/diff/svn/DiffusionSvnDiffQuery.php
index e56be33a90..3824c74df1 100644
--- a/src/applications/diffusion/query/diff/svn/DiffusionSvnDiffQuery.php
+++ b/src/applications/diffusion/query/diff/svn/DiffusionSvnDiffQuery.php
@@ -22,15 +22,14 @@ final class DiffusionSvnDiffQuery extends DiffusionDiffQuery {
     $drequest = $this->getRequest();
     $repository = $drequest->getRepository();
 
-    if (!$drequest->getRawCommit()) {
-      $effective_commit = $this->getEffectiveCommit();
-      if (!$effective_commit) {
-        return null;
-      }
-      // TODO: Sketchy side effect.
-      $drequest->setCommit($effective_commit);
+    $effective_commit = $this->getEffectiveCommit();
+    if (!$effective_commit) {
+      return null;
     }
 
+    $drequest = clone $drequest;
+    $drequest->setCommit($effective_commit);
+
     $path_change_query = DiffusionPathChangeQuery::newFromDiffusionRequest(
       $drequest);
     $path_changes = $path_change_query->loadChanges();
diff --git a/src/applications/diffusion/query/lastmodified/base/DiffusionLastModifiedQuery.php b/src/applications/diffusion/query/lastmodified/base/DiffusionLastModifiedQuery.php
index 4f5a3c4aee..9359266952 100644
--- a/src/applications/diffusion/query/lastmodified/base/DiffusionLastModifiedQuery.php
+++ b/src/applications/diffusion/query/lastmodified/base/DiffusionLastModifiedQuery.php
@@ -1,7 +1,7 @@
 <?php
 
 /*
- * Copyright 2011 Facebook, Inc.
+ * Copyright 2012 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,49 +16,15 @@
  * limitations under the License.
  */
 
-abstract class DiffusionLastModifiedQuery {
-
-  private $request;
-
-  final private function __construct() {
-    // <private>
-  }
+abstract class DiffusionLastModifiedQuery extends DiffusionQuery {
 
   final public static function newFromDiffusionRequest(
     DiffusionRequest $request) {
-
-    $repository = $request->getRepository();
-
-    switch ($repository->getVersionControlSystem()) {
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_GIT:
-        $class = 'DiffusionGitLastModifiedQuery';
-        break;
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_MERCURIAL:
-        $class = 'DiffusionMercurialLastModifiedQuery';
-        break;
-      case PhabricatorRepositoryType::REPOSITORY_TYPE_SVN:
-        $class = 'DiffusionSvnLastModifiedQuery';
-        break;
-      default:
-        throw new Exception("Unsupported VCS!");
-    }
-
-    PhutilSymbolLoader::loadClass($class);
-    $query = new $class();
-
-    $query->request = $request;
-
-    return $query;
-  }
-
-  final protected function getRequest() {
-    return $this->request;
+    return parent::newQueryObject(__CLASS__, $request);
   }
 
   final public function loadLastModification() {
     return $this->executeQuery();
   }
 
-  abstract protected function executeQuery();
-
 }
diff --git a/src/applications/diffusion/query/lastmodified/base/__init__.php b/src/applications/diffusion/query/lastmodified/base/__init__.php
index 201f669215..de060b1f6b 100644
--- a/src/applications/diffusion/query/lastmodified/base/__init__.php
+++ b/src/applications/diffusion/query/lastmodified/base/__init__.php
@@ -6,9 +6,7 @@
 
 
 
-phutil_require_module('phabricator', 'applications/repository/constants/repositorytype');
-
-phutil_require_module('phutil', 'symbols');
+phutil_require_module('phabricator', 'applications/diffusion/query/base');
 
 
 phutil_require_source('DiffusionLastModifiedQuery.php');
diff --git a/src/applications/diffusion/query/lastmodified/svn/DiffusionSvnLastModifiedQuery.php b/src/applications/diffusion/query/lastmodified/svn/DiffusionSvnLastModifiedQuery.php
index 513b72550b..c6c1e4b6f4 100644
--- a/src/applications/diffusion/query/lastmodified/svn/DiffusionSvnLastModifiedQuery.php
+++ b/src/applications/diffusion/query/lastmodified/svn/DiffusionSvnLastModifiedQuery.php
@@ -1,7 +1,7 @@
 <?php
 
 /*
- * Copyright 2011 Facebook, Inc.
+ * Copyright 2012 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,6 +30,11 @@ final class DiffusionSvnLastModifiedQuery extends DiffusionLastModifiedQuery {
     $history_query->needChildChanges(true);
     $history_query->needDirectChanges(true);
     $history_array = $history_query->loadHistory();
+
+    if (!$history_array) {
+      return array(null, null);
+    }
+
     $history = reset($history_array);
 
     return array($history->getCommit(), $history->getCommitData());