In English, the causation verbs 'make' and 'let' allow their following VP to be omitted: 'I made/let Chris play the drums before I made/let Sam (play the drums)'. We show that such 'causative VP-omission' involves Null Complement Anaphora rather than Predicate Ellipsis, and requires an agentive causee. We analyse this restriction — which extends to Null Complement Anaphora with aspectual verbs — as resulting from an interaction between a non-stative null pro-form and Voice (cf. Folli and Harley 2005).