diff --git a/collects/typed-scheme/typecheck/tc-expr-unit.ss b/collects/typed-scheme/typecheck/tc-expr-unit.ss
index c61bbd3d..b9c97d48 100644
--- a/collects/typed-scheme/typecheck/tc-expr-unit.ss
+++ b/collects/typed-scheme/typecheck/tc-expr-unit.ss
@@ -46,6 +46,7 @@
     [else Univ]))
 
 
+;; do-inst : syntax type -> type
 (define (do-inst stx ty)
   (define inst (syntax-property stx 'type-inst))
   (define (split-last l)
@@ -53,16 +54,16 @@
       (values all-but (car last-list))))
   (cond [(not inst) ty]
         [(not (or (Poly? ty) (PolyDots? ty)))
-         (tc-error/expr #:return (ret (Un)) "Cannot instantiate non-polymorphic type ~a" ty)]
+         (tc-error/expr #:return (Un) "Cannot instantiate non-polymorphic type ~a" ty)]
         
         [(and (Poly? ty)
               (not (= (length (syntax->list inst)) (Poly-n ty))))
-         (tc-error/expr #:return (ret (Un)) 
+         (tc-error/expr #:return (Un)
                         "Wrong number of type arguments to polymorphic type ~a:~nexpected: ~a~ngot: ~a"
                         ty (Poly-n ty) (length (syntax->list inst)))]
         [(and (PolyDots? ty) (not (>= (length (syntax->list inst)) (sub1 (PolyDots-n ty)))))
          ;; we can provide 0 arguments for the ... var
-         (tc-error/expr #:return (ret (Un)) 
+         (tc-error/expr #:return (Un)
                         "Wrong number of type arguments to polymorphic type ~a:~nexpected at least: ~a~ngot: ~a"
                         ty (sub1 (PolyDots-n ty)) (length (syntax->list inst)))]
         [(PolyDots? ty)