Résumé : TLA+ is a formal specification language that is based on Zermelo-Fränkel set theory and the Temporal Logic of Actions TLA. The TLA+ proof system TLAPS assists users in deductively verifying safety properties of TLA+ specifications. TLAPS is built around a proof manager, which interprets the TLA+ proof language, generates corresponding proof obligations, and passes them to backend verifiers. In this paper we present a new backend for use with SMT solvers that supports elementary set theory, functions, arithmetic, tuples, and records. We introduce a typing discipline for TLA+ proof obligations, which helps us to disambiguate the translation of expressions of (untyped) TLA+, while ensuring its soundness. Our work is a first step towards the certification of proofs generated by proof-producing SMT solvers in Isabelle/TLA+, which is intended to be the only trusted component of TLAPS.