diff --git a/src/libsystemd-network/sd-dhcp6-client.c b/src/libsystemd-network/sd-dhcp6-client.c
index 606e48ce6f..b774772229 100644
--- a/src/libsystemd-network/sd-dhcp6-client.c
+++ b/src/libsystemd-network/sd-dhcp6-client.c
@@ -779,7 +779,7 @@ int dhcp6_client_send_message(sd_dhcp6_client *client) {
         if (r < 0)
                 return r;
 
-        assert(client->duid_len);
+        assert(client->duid_len > 0);
         r = dhcp6_option_append(&opt, &optlen, SD_DHCP6_OPTION_CLIENTID,
                                 client->duid_len, &client->duid);
         if (r < 0)