diff --git a/builtin/rebase--interactive.c b/builtin/rebase--interactive.c
index 551faba558..4b9d2a07cb 100644
--- a/builtin/rebase--interactive.c
+++ b/builtin/rebase--interactive.c
@@ -181,8 +181,9 @@ int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
 		OPT_STRING(0, "upstream", &upstream, N_("upstream"),
 			   N_("the upstream commit")),
 		OPT_STRING(0, "head-name", &head_name, N_("head-name"), N_("head name")),
-		OPT_STRING('S', "gpg-sign", &opts.gpg_sign, N_("gpg-sign"),
-			   N_("GPG-sign commits")),
+		{ OPTION_STRING, 'S', "gpg-sign", &opts.gpg_sign, N_("key-id"),
+			N_("GPG-sign commits"),
+			PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 		OPT_STRING(0, "strategy", &opts.strategy, N_("strategy"),
 			   N_("rebase strategy")),
 		OPT_STRING(0, "strategy-opts", &raw_strategies, N_("strategy-opts"),