diff --git a/src/repository/api/ArcanistMercurialAPI.php b/src/repository/api/ArcanistMercurialAPI.php
index 2d7484a8..ba2f2b4e 100644
--- a/src/repository/api/ArcanistMercurialAPI.php
+++ b/src/repository/api/ArcanistMercurialAPI.php
@@ -139,7 +139,7 @@ final class ArcanistMercurialAPI extends ArcanistRepositoryAPI {
     }
 
     if ($this->getBaseCommitArgumentRules() ||
-        $this->getWorkingCopyIdentity()->getConfigFromAnySource('base')) {
+        $this->getConfigurationManager()->getConfigFromAnySource('base')) {
       $base = $this->resolveBaseCommit();
       if (!$base) {
         throw new ArcanistUsageException(