diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 6b4ee8a31b..1391316cde 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -1777,7 +1777,7 @@ struct submodule_update_clone {
 	int current;
 
 	/* configuration parameters which are passed on to the children */
-	struct update_data *update_data;
+	const struct update_data *update_data;
 
 	/* to be consumed by update_submodule() */
 	struct update_clone_data *update_clone;
@@ -1862,7 +1862,7 @@ static int prepare_to_clone_next_submodule(const struct cache_entry *ce,
 	const char *update_string;
 	enum submodule_update_type update_type;
 	char *key;
-	struct update_data *ud = suc->update_data;
+	const struct update_data *ud = suc->update_data;
 	char *displaypath = get_submodule_displaypath(ce->name, ud->prefix);
 	struct strbuf sb = STRBUF_INIT;
 	int needs_cloning = 0;