The lockout can be problematic for some people. One of two scenarios usually plays out:

  1. Substituting excessive lumbar extension for hip extension.
  2. Butt-sticking-out syndrome.

In either case the cue I use is to "finish tall" or "stand tall" or "stop doing that because my eyes hurt." The goal is to finish with the hips (squeeze the glutes) at the top.

Related:  30 Days of Deadlifts

Related:  Master This Before You Deadlift