diff --git a/parse-options-cb.c b/parse-options-cb.c
index db6f666ef7..7d56681130 100644
--- a/parse-options-cb.c
+++ b/parse-options-cb.c
@@ -181,7 +181,8 @@ struct option *parse_options_dup(const struct option *o)
 	return opts;
 }
 
-struct option *parse_options_concat(struct option *a, struct option *b)
+struct option *parse_options_concat(const struct option *a,
+				    const struct option *b)
 {
 	struct option *ret;
 	size_t a_len = parse_options_count(a);
diff --git a/parse-options.h b/parse-options.h
index fdc0c1cb97..1d60205881 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -281,7 +281,7 @@ int parse_options_step(struct parse_opt_ctx_t *ctx,
 int parse_options_end(struct parse_opt_ctx_t *ctx);
 
 struct option *parse_options_dup(const struct option *a);
-struct option *parse_options_concat(struct option *a, struct option *b);
+struct option *parse_options_concat(const struct option *a, const struct option *b);
 
 /*----- some often used options -----*/
 int parse_opt_abbrev_cb(const struct option *, const char *, int);