MuSig is a multi-signature scheme for Schnorr signatures, which supports key aggregation and is secure in the plain public key model. Standard derandomization techniques for discrete logarithm-based signatures such as RFC~6979, which make the signing procedure immune to catastrophic failures in the randomness generation, are not applicable to multi-signatures as an attacker could trick an honest user into producing two different partial signatures with the same randomness, which would reveal the user's secret key.