diff --git a/src/repository/api/ArcanistGitAPI.php b/src/repository/api/ArcanistGitAPI.php
index dca9fbfd..11a36742 100644
--- a/src/repository/api/ArcanistGitAPI.php
+++ b/src/repository/api/ArcanistGitAPI.php
@@ -535,7 +535,9 @@ final class ArcanistGitAPI extends ArcanistRepositoryAPI {
       $stdout = $this->getHashFromFromSVNRevisionNumber($match[1]);
     } else {
       list($stdout) = $this->execxLocal(
-        'show -s --format=%s %s --',
+        phutil_is_windows()
+        ? 'show -s --format=%C %s --'
+        : 'show -s --format=%s %s --',
         '%H',
         $string);
     }