diff --git a/environment.c b/environment.c
index cdc097f80c..6a8e0c2d1b 100644
--- a/environment.c
+++ b/environment.c
@@ -167,8 +167,11 @@ static void setup_git_env(void)
 	const char *replace_ref_base;
 
 	git_dir = getenv(GIT_DIR_ENVIRONMENT);
-	if (!git_dir)
+	if (!git_dir) {
+		if (!startup_info->have_repository)
+			die("BUG: setup_git_env called without repository");
 		git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
+	}
 	gitfile = read_gitfile(git_dir);
 	git_dir = xstrdup(gitfile ? gitfile : git_dir);
 	if (get_common_dir(&sb, git_dir))