Dependently typed languages such as Coq or Agda are very convenient tools to program with strong invariants and develop mathematical proofs. However, a user might be inconvenienced by things such as the fact that n and n+0 are not considered definitionally equal, or the inability to postulate one's own constructs with computation rules such as exceptions [PT18]. Coq modulo theory [Str10] solves the first of the two problems by extending Coq's conversion with decision procedures, e.g., for linear integer arithmetic. Rewrite rules can be used to deal with directed equalities for natural numbers, but also to implement exceptions that compute. They were introduced in Agda [CA16] a few years ago, and later extended to provide more guarantees with a modular confluence checker [CTW19, CTW21]. We present a work-in-progress extension 1 of Coq which supports user-defined rewrite rules. While we mostly follow in the footsteps of the Agda implementation, we also have to face new issues due to the differences in the implementation and meta-theory of Coq and Agda. The most prominent one being the different treatment of universes as Coq supports cumulativity but no first-class universe levels. We will take advantage of this talk to expose our ideas on how to solve the different issues that arise when adding user-defined rewrite rules to a proof assistant by integrating 2 rewrite rules in MetaCoq [SAB + 20, SBF + 20], building on previous work [CTW19, CTW21].