CHE channel for the formation of double-BHs, including the occurrence of an overcontact phase as in Marchant et al. (2016). Numbers correspond to a system with Z = Z_⊙/ 50, initial masses M₁ = 70 M_⊙ and M₂ = 56 M_⊙, and a very short initial period at the zero-age main sequence (ZAMS). This system evolves early on into a contact configuration where mass is transferred back and forth until a mass ratio of unity is achieved. Efficient rotational mixing distributes the helium-rich material from the core throughout the entire envelope, resulting in an almost pure helium star at the terminal-age main sequence (TAMS). Depending on the final masses of each component, the system may then proceed to form a compact BH binary that can merge within a Hubble time, or explode as a PISNe. The models from Marchant et al. (2016) had an error in the computation of spin-orbit coupling which resulted in slightly wider orbits. We have corrected for this, so the values differ slightly from those in Marchant et al. (2016). We have also verified that the conclusions of that work remain valid despite this issue.