diff --git a/setup.c b/setup.c
index c248845aba21d9..b76399d6081cbf 100644
--- a/setup.c
+++ b/setup.c
@@ -889,7 +889,7 @@ static enum discovery_result setup_git_directory_gently_1(struct strbuf *dir,
 	const char *env_ceiling_dirs = getenv(CEILING_DIRECTORIES_ENVIRONMENT);
 	struct string_list ceiling_dirs = STRING_LIST_INIT_DUP;
 	const char *gitdirenv;
-	int ceil_offset = -1, min_offset = has_dos_drive_prefix(dir->buf) ? 3 : 1;
+	int ceil_offset = -1, min_offset = offset_1st_component(dir->buf);
 	dev_t current_device = 0;
 	int one_filesystem = 1;