diff --git a/ls-refs.c b/ls-refs.c
index 07429f3a1c..883c0c58b2 100644
--- a/ls-refs.c
+++ b/ls-refs.c
@@ -170,6 +170,8 @@ int ls_refs(struct repository *r, struct packet_reader *request)
 		}
 		else if (!strcmp("unborn", arg))
 			data.unborn = allow_unborn;
+		else
+			die(_("unexpected line: '%s'"), arg);
 	}
 
 	if (request->status != PACKET_READ_FLUSH)
diff --git a/t/t5701-git-serve.sh b/t/t5701-git-serve.sh
index 3928424e1b..aa1827d841 100755
--- a/t/t5701-git-serve.sh
+++ b/t/t5701-git-serve.sh
@@ -147,6 +147,19 @@ test_expect_success 'basics of ls-refs' '
 	test_cmp expect actual
 '
 
+test_expect_success 'ls-refs complains about unknown options' '
+	test-tool pkt-line pack >in <<-EOF &&
+	command=ls-refs
+	object-format=$(test_oid algo)
+	0001
+	no-such-arg
+	0000
+	EOF
+
+	test_must_fail test-tool serve-v2 --stateless-rpc 2>err <in &&
+	grep unexpected.line.*no-such-arg err
+'
+
 test_expect_success 'basic ref-prefixes' '
 	test-tool pkt-line pack >in <<-EOF &&
 	command=ls-refs