diff --git a/src/repository/api/ArcanistSubversionAPI.php b/src/repository/api/ArcanistSubversionAPI.php
--- a/src/repository/api/ArcanistSubversionAPI.php
+++ b/src/repository/api/ArcanistSubversionAPI.php
@@ -651,7 +651,7 @@
     $results = $conduit->callMethodSynchronous('differential.query', $query);
 
     foreach ($results as $key => $result) {
-      if ($result['sourcePath'] != $this->getPath()) {
+      if (idx($result, 'sourcePath') != $this->getPath()) {
         unset($results[$key]);
       }
     }