In this paper we obtain a Wiener-Hopf type factorization for a time-inhomogeneous arithmetic Brownian motion with deterministic time-dependent drift and volatility. To the best of our knowledge, this paper is the very first step towards realizing the objective of deriving Wiener-Hopf type factorizations for (real-valued) time-inhomogeneous Lévy processes. In particular, we argue that the classical Wiener-Hopf factorization for time-homogeneous Lévy processes quite likely does not carry over to the case of time-inhomogeneous Lévy processes.