diff --git a/builtin/rebase.c b/builtin/rebase.c
index 06f6490..3b9da69 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -198,7 +198,7 @@
 static int do_interactive_rebase(struct replay_opts *opts, unsigned flags,
 				 const char *switch_to, struct commit *upstream,
 				 struct commit *onto, const char *onto_name,
-				 const char *squash_onto, const char *head_name,
+				 struct object_id *squash_onto, const char *head_name,
 				 struct commit *restrict_revision, char *raw_strategies,
 				 struct string_list *commands, unsigned autosquash)
 {
@@ -226,7 +226,8 @@
 	}
 
 	if (!upstream && squash_onto)
-		write_file(path_squash_onto(), "%s\n", squash_onto);
+		write_file(path_squash_onto(), "%s\n",
+			   oid_to_hex(squash_onto));
 
 	argv_array_pushl(&make_script_args, "", revisions, NULL);
 	if (restrict_revision)
@@ -267,10 +268,11 @@
 	struct replay_opts opts = REPLAY_OPTS_INIT;
 	unsigned flags = 0, keep_empty = 0, rebase_merges = 0, autosquash = 0;
 	int abbreviate_commands = 0, rebase_cousins = -1, ret = 0;
-	const char *onto_name = NULL,
-		*squash_onto = NULL, *head_name = NULL,
-		*switch_to = NULL, *cmd = NULL;
+	const char *onto_name = NULL, *head_name = NULL, *switch_to = NULL,
+		*cmd = NULL;
 	struct commit *onto = NULL, *upstream = NULL, *restrict_revision = NULL;
+	struct object_id squash_onto = null_oid;
+	struct object_id *squash_onto_opt = NULL;
 	struct string_list commands = STRING_LIST_INIT_DUP;
 	char *raw_strategies = NULL;
 	enum {
@@ -311,8 +313,8 @@
 		{ OPTION_CALLBACK, 0, "restrict-revision", &restrict_revision,
 		  N_("restrict-revision"), N_("restrict revision"),
 		  PARSE_OPT_NONEG, parse_opt_commit, 0 },
-		OPT_STRING(0, "squash-onto", &squash_onto, N_("squash-onto"),
-			   N_("squash onto")),
+		{ OPTION_CALLBACK, 0, "squash-onto", &squash_onto, N_("squash-onto"),
+		  N_("squash onto"), PARSE_OPT_NONEG, parse_opt_object_id, 0 },
 		{ OPTION_CALLBACK, 0, "upstream", &upstream, N_("upstream"),
 		  N_("the upstream commit"), PARSE_OPT_NONEG, parse_opt_commit,
 		  0 },
@@ -349,6 +351,9 @@
 
 	opts.gpg_sign = xstrdup_or_null(opts.gpg_sign);
 
+	if (!is_null_oid(&squash_onto))
+		squash_onto_opt = &squash_onto;
+
 	flags |= keep_empty ? TODO_LIST_KEEP_EMPTY : 0;
 	flags |= abbreviate_commands ? TODO_LIST_ABBREVIATE_CMDS : 0;
 	flags |= rebase_merges ? TODO_LIST_REBASE_MERGES : 0;
@@ -373,7 +378,7 @@
 			die(_("a base commit must be provided with --upstream or --onto"));
 
 		ret = do_interactive_rebase(&opts, flags, switch_to, upstream, onto,
-					    onto_name, squash_onto, head_name, restrict_revision,
+					    onto_name, squash_onto_opt, head_name, restrict_revision,
 					    raw_strategies, &commands, autosquash);
 		break;
 	case SKIP: {
diff --git a/parse-options-cb.c b/parse-options-cb.c
index 2206eb7..28ad5cd 100644
--- a/parse-options-cb.c
+++ b/parse-options-cb.c
@@ -129,6 +129,23 @@
 	return 0;
 }
 
+int parse_opt_object_id(const struct option *opt, const char *arg, int unset)
+{
+	struct object_id oid;
+	struct object_id *target = opt->value;
+
+	if (unset) {
+		*target = null_oid;
+		return 0;
+	}
+	if (!arg)
+		return -1;
+	if (get_oid(arg, &oid))
+		return error(_("malformed object name '%s'"), arg);
+	*target = oid;
+	return 0;
+}
+
 int parse_opt_tertiary(const struct option *opt, const char *arg, int unset)
 {
 	int *target = opt->value;
diff --git a/parse-options.h b/parse-options.h
index 5a75646..0ab1103 100644
--- a/parse-options.h
+++ b/parse-options.h
@@ -264,7 +264,10 @@
 int parse_opt_expiry_date_cb(const struct option *, const char *, int);
 int parse_opt_color_flag_cb(const struct option *, const char *, int);
 int parse_opt_verbosity_cb(const struct option *, const char *, int);
+/* value is struct oid_array* */
 int parse_opt_object_name(const struct option *, const char *, int);
+/* value is struct object_id* */
+int parse_opt_object_id(const struct option *, const char *, int);
 int parse_opt_commits(const struct option *, const char *, int);
 int parse_opt_commit(const struct option *, const char *, int);
 int parse_opt_tertiary(const struct option *, const char *, int);