diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
index 99b39faa49..7fc1ec5e13 100644
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -391,6 +391,7 @@ phutil_register_library_map(array(
     'DifferentialPathFieldSpecification' => 'applications/differential/field/specification/DifferentialPathFieldSpecification.php',
     'DifferentialPeopleMenuEventListener' => 'applications/differential/events/DifferentialPeopleMenuEventListener.php',
     'DifferentialPrimaryPaneView' => 'applications/differential/view/DifferentialPrimaryPaneView.php',
+    'DifferentialRawDiffRenderer' => 'applications/differential/render/DifferentialRawDiffRenderer.php',
     'DifferentialReleephRequestFieldSpecification' => 'applications/releeph/differential/DifferentialReleephRequestFieldSpecification.php',
     'DifferentialRemarkupRule' => 'applications/differential/remarkup/DifferentialRemarkupRule.php',
     'DifferentialReplyHandler' => 'applications/differential/mail/DifferentialReplyHandler.php',
diff --git a/src/applications/differential/mail/DifferentialReviewRequestMail.php b/src/applications/differential/mail/DifferentialReviewRequestMail.php
index 2c858de252..82a58c8c70 100644
--- a/src/applications/differential/mail/DifferentialReviewRequestMail.php
+++ b/src/applications/differential/mail/DifferentialReviewRequestMail.php
@@ -104,38 +104,16 @@ abstract class DifferentialReviewRequestMail extends DifferentialMail {
   }
 
   private function buildPatch() {
-    $diff = new DifferentialDiff();
-    $diff->attachChangesets($this->getChangesets());
-    foreach ($diff->getChangesets() as $changeset) {
-      $changeset->attachHunks(
-        $changeset->loadRelatives(new DifferentialHunk(), 'changesetID'));
-    }
-
-    $raw_changes = $diff->buildChangesList();
-    $changes = array();
-    foreach ($raw_changes as $changedict) {
-      $changes[] = ArcanistDiffChange::newFromDictionary($changedict);
-    }
+    $renderer = new DifferentialRawDiffRenderer();
+    $renderer->setChangesets($this->getChangesets());
+    $renderer->setFormat(
+      PhabricatorEnv::getEnvConfig('metamta.differential.patch-format'));
 
     // TODO: It would be nice to have a real viewer here eventually, but
     // in the meantime anyone we're sending mail to can certainly see the
     // patch.
-    $loader = id(new PhabricatorFileBundleLoader())
-      ->setViewer(PhabricatorUser::getOmnipotentUser());
-
-    $bundle = ArcanistBundle::newFromChanges($changes);
-    $bundle->setLoadFileDataCallback(array($loader, 'loadFileData'));
-
-    $format = PhabricatorEnv::getEnvConfig('metamta.differential.patch-format');
-    switch ($format) {
-      case 'git':
-        return $bundle->toGitPatch();
-        break;
-      case 'unified':
-      default:
-        return $bundle->toUnifiedDiff();
-        break;
-    }
+    $renderer->setViewer(PhabricatorUser::getOmnipotentUser());
+    return $renderer->buildPatch();
   }
 
   protected function getMailTags() {
diff --git a/src/applications/differential/render/DifferentialRawDiffRenderer.php b/src/applications/differential/render/DifferentialRawDiffRenderer.php
new file mode 100644
index 0000000000..e8a1d09a60
--- /dev/null
+++ b/src/applications/differential/render/DifferentialRawDiffRenderer.php
@@ -0,0 +1,69 @@
+<?php
+final class DifferentialRawDiffRenderer {
+
+  private $changesets;
+  private $format = 'unified';
+  private $viewer;
+
+  public function setFormat($format) {
+    $this->format = $format;
+    return $this;
+  }
+
+  public function getFormat() {
+    return $this->format;
+  }
+
+  public function setChangesets(array $changesets) {
+    assert_instances_of($changesets, 'DifferentialChangeset');
+
+    $this->changesets = $changesets;
+    return $this;
+  }
+
+  public function getChangesets() {
+    return $this->changesets;
+  }
+
+  public function setViewer(PhabricatorUser $viewer) {
+    $this->viewer = $viewer;
+    return $this;
+  }
+
+  public function getViewer() {
+    return $this->viewer;
+  }
+
+  public function buildPatch() {
+    $diff = new DifferentialDiff();
+    $diff->attachChangesets($this->getChangesets());
+    foreach ($diff->getChangesets() as $changeset) {
+      $changeset->attachHunks(
+        $changeset->loadRelatives(new DifferentialHunk(), 'changesetID'));
+    }
+
+    $raw_changes = $diff->buildChangesList();
+    $changes = array();
+    foreach ($raw_changes as $changedict) {
+      $changes[] = ArcanistDiffChange::newFromDictionary($changedict);
+    }
+
+    $viewer = $this->getViewer();
+    $loader = id(new PhabricatorFileBundleLoader())
+      ->setViewer($viewer);
+
+    $bundle = ArcanistBundle::newFromChanges($changes);
+    $bundle->setLoadFileDataCallback(array($loader, 'loadFileData'));
+
+    $format = $this->getFormat();
+    switch ($format) {
+      case 'git':
+        return $bundle->toGitPatch();
+        break;
+      case 'unified':
+      default:
+        return $bundle->toUnifiedDiff();
+        break;
+    }
+  }
+}