diff --git a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
--- a/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
+++ b/src/applications/diffusion/engine/DiffusionCommitHookEngine.php
@@ -1212,7 +1212,7 @@
 
     if (!strlen($raw_diff)) {
       // If the commit is actually empty, just return no changesets.
-      return array();
+      return array(array(), 0);
     }
 
     $parser = new ArcanistDiffParser();