diff --git a/src/util-io.c b/src/util-io.c
index c873c02..0fd7ae7 100644
--- a/src/util-io.c
+++ b/src/util-io.c
@@ -281,7 +281,7 @@ int
 iobuf_append_fd(struct iobuf *buf, int fd)
 {
 	/* Array must remain terminated by -1 */
-	for (size_t idx = 0; idx < sizeof(buf->fds) - 1; idx ++) {
+	for (size_t idx = 0; idx < ARRAY_LENGTH(buf->fds) - 1; idx ++) {
 		if (buf->fds[idx] == -1) {
 			int f = dup(fd);
 			if (f == -1)
@@ -629,6 +629,29 @@ MUNIT_TEST(test_iobuf_append_fd)
 	return MUNIT_OK;
 }
 
+MUNIT_TEST(test_iobuf_append_fd_too_many)
+{
+	_cleanup_fclose_ FILE *fp = tmpfile();
+	int fd = fileno(fp);
+
+	_cleanup_iobuf_ struct iobuf *buf = iobuf_new(20);
+	const size_t nfds = ARRAY_LENGTH(buf->fds);
+	int *last_fd = &buf->fds[nfds - 1]; /* always -1 */
+	int err = 0;
+	size_t count = 0;
+
+	/* 32 fds hardcoded in the struct, last one is always -1 */
+	for (count = 0; err == 0 && count < nfds + 1; count++) {
+		err = iobuf_append_fd(buf, fd);
+		munit_assert_int(*last_fd, ==, -1);
+	}
+
+	munit_assert_int(count, ==, 32);
+	munit_assert_int(err, ==, -ENOMEM);
+
+	return MUNIT_OK;
+}
+
 MUNIT_TEST(test_iobuf_recv_fd)
 {
 	int fds[2];