Our idiomatically objectionable title is a pun on Milner's well-typed programs do not go wrong'' --- because we provide a completeness result for type-checking rather than a soundness result. We show that the well-behaved functions of untyped PCF are already expressible in typed PCF: any equivalence class of the partial logical equivalence generated from the flat natural numbers in the model given by PCF's operational semantics is inhabited by a well-typed term.