diff --git a/pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/typecheck/tc-expr-unit.rkt b/pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/typecheck/tc-expr-unit.rkt
index 02468fa093..dc1f0858ff 100644
--- a/pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/typecheck/tc-expr-unit.rkt
+++ b/pkgs/typed-racket-pkgs/typed-racket-lib/typed-racket/typecheck/tc-expr-unit.rkt
@@ -48,9 +48,6 @@
 ;; do-normal-inst : Syntax (Option Syntax) Type -> Type
 ;; Instantiate a normal polymorphic type
 (define (do-normal-inst stx inst ty)
-  (define (split-last l)
-    (let-values ([(all-but last-list) (split-at l (sub1 (length l)))])
-      (values all-but (car last-list))))
   (match ty
     [(list ty)
      (list
@@ -73,22 +70,18 @@
           ;; In this case, we need to check the last thing.  If it's a dotted var, then we need to
           ;; use instantiate-poly-dotted, otherwise we do the normal thing.
           ;; In the case that the list is empty we also do the normal thing
-          (let ((stx-list (syntax->list inst)))
-            (if (null? stx-list)
-                (instantiate-poly ty (map parse-type stx-list))
-                (let-values ([(all-but-last last-stx) (split-last stx-list)])
-                  (match (syntax-e last-stx)
-                    [(cons last-ty-stx (? identifier? last-id-stx))
-                     (unless (bound-index? (syntax-e last-id-stx))
-                       (tc-error/stx last-id-stx "~a is not a type variable bound with ..." (syntax-e last-id-stx)))
-                     (if (= (length all-but-last) (sub1 (PolyDots-n ty)))
-                         (let* ([last-id (syntax-e last-id-stx)]
-                                [last-ty (extend-tvars (list last-id) (parse-type last-ty-stx))])
-                           (instantiate-poly-dotted ty (map parse-type all-but-last) last-ty last-id))
-                         (tc-error/expr #:return (Un) "Wrong number of fixed type arguments to polymorphic type ~a:\nexpected: ~a\ngot: ~a"
-                                        ty (sub1 (PolyDots-n ty)) (length all-but-last)))]
-                    [_
-                     (instantiate-poly ty (map parse-type stx-list))]))))]
+          (match (syntax->list inst)
+            [(list ty-stxs ... (app syntax-e (cons bound-ty-stx (? identifier? bound-id))))
+             (unless (bound-index? (syntax-e bound-id))
+               (tc-error/stx bound-id "~a is not a type variable bound with ..." (syntax-e bound-id)))
+             (if (= (length ty-stxs) (sub1 (PolyDots-n ty)))
+                 (let* ([last-id (syntax-e bound-id)]
+                        [last-ty (extend-tvars (list last-id) (parse-type bound-ty-stx))])
+                   (instantiate-poly-dotted ty (map parse-type ty-stxs) last-ty last-id))
+                 (tc-error/expr #:return (Un) "Wrong number of fixed type arguments to polymorphic type ~a:\nexpected: ~a\ngot: ~a"
+                                ty (sub1 (PolyDots-n ty)) (length ty-stxs)))]
+            [stx-list
+             (instantiate-poly ty (map parse-type stx-list))])]
          [else
           (instantiate-poly ty (stx-map parse-type inst))]))]
     [_ (if inst