aneks ugovora

1. contract annex; addendum to a contract
   Za novog cimera moramo da potpišemo aneks ugovora o zakupu. — For the new flatmate we have to sign an addendum to the lease.
   Gazda je novu kiriju uneo u aneks ugovora. — The landlord put the new rent into the contract annex.

In speech people often just say "aneks"; the contract's name follows in the genitive: aneks ugovora o zakupu.