diff --git a/src/applications/differential/conduit/DifferentialParseCommitMessageConduitAPIMethod.php b/src/applications/differential/conduit/DifferentialParseCommitMessageConduitAPIMethod.php
--- a/src/applications/differential/conduit/DifferentialParseCommitMessageConduitAPIMethod.php
+++ b/src/applications/differential/conduit/DifferentialParseCommitMessageConduitAPIMethod.php
@@ -33,7 +33,7 @@
       new DifferentialRevision(),
       DifferentialCustomField::ROLE_COMMITMESSAGE);
     $field_list->setViewer($viewer);
-    $field_map = mpull($field_list, null, 'getFieldKeyForConduit');
+    $field_map = mpull($field_list->getFields(), null, 'getFieldKeyForConduit');
 
     $corpus_map = $this->parseCommitMessage($corpus);