diff --git a/src/libfetchers/git-utils.cc b/src/libfetchers/git-utils.cc
index 54f6b4b51..2dd3eeb5c 100644
--- a/src/libfetchers/git-utils.cc
+++ b/src/libfetchers/git-utils.cc
@@ -417,7 +417,7 @@ struct GitRepoImpl : GitRepo, std::enable_shared_from_this<GitRepoImpl>
         //       then use code that was removed in this commit (see blame)
 
         auto dir = this->path;
-        Strings gitArgs{"-C", dir.string(), "fetch", "--quiet", "--force"};
+        Strings gitArgs{"-C", dir.string(), "--git-dir", ".", "fetch", "--quiet", "--force"};
         if (shallow)
             append(gitArgs, {"--depth", "1"});
         append(gitArgs, {std::string("--"), url, refspec});