diff --git a/src/libfetchers/git-utils.cc b/src/libfetchers/git-utils.cc
index 3b15a85ce..6a75daf61 100644
--- a/src/libfetchers/git-utils.cc
+++ b/src/libfetchers/git-utils.cc
@@ -545,7 +545,7 @@ 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});
diff --git a/tests/functional/common/vars.sh b/tests/functional/common/vars.sh
index 4b88e8526..ed4b47727 100644
--- a/tests/functional/common/vars.sh
+++ b/tests/functional/common/vars.sh
@@ -60,6 +60,7 @@ unset XDG_DATA_HOME
 unset XDG_CONFIG_HOME
 unset XDG_CONFIG_DIRS
 unset XDG_CACHE_HOME
+unset GIT_DIR
 
 export IMPURE_VAR1=foo
 export IMPURE_VAR2=bar