diff --git a/collects/tests/typed-racket/fail/plambda-dup-tvar.rkt b/collects/tests/typed-racket/fail/plambda-dup-tvar.rkt
new file mode 100644
index 00000000..9cf2889d
--- /dev/null
+++ b/collects/tests/typed-racket/fail/plambda-dup-tvar.rkt
@@ -0,0 +1,9 @@
+#;
+(exn-pred exn:fail:syntax?)
+#lang typed/racket
+
+;; don't allow duplicate type variable names
+
+(plambda: (a a a) ([x : a]) x)
+(popt-lambda: (a a a) ([x : a]) x)
+(pcase-lambda: (a a a) ([x : a]) x)
diff --git a/collects/tests/typed-racket/fail/poly-dup-name.rkt b/collects/tests/typed-racket/fail/poly-dup-name.rkt
new file mode 100644
index 00000000..e88d8937
--- /dev/null
+++ b/collects/tests/typed-racket/fail/poly-dup-name.rkt
@@ -0,0 +1,8 @@
+#;
+(exn:pred (lambda (e) (regexp-match? "duplicate type variable" e)))
+#lang typed/racket
+
+;; don't allow duplicate type variable names
+
+(: f (All (A A) (A -> (List A))))
+(define (f a) (list a))
diff --git a/collects/tests/typed-racket/fail/polydots-dup-name.rkt b/collects/tests/typed-racket/fail/polydots-dup-name.rkt
new file mode 100644
index 00000000..5fa6e21b
--- /dev/null
+++ b/collects/tests/typed-racket/fail/polydots-dup-name.rkt
@@ -0,0 +1,10 @@
+#;
+(exn:pred (lambda (e) (regexp-match? "duplicate type variable or index" e)))
+#lang typed/racket
+
+;; don't allow duplicate names in indexes and tvars
+
+(: f (All (A A ...) (A A ... A -> (List A ... A))))
+
+(define (f a . xs)
+  (map (λ: ([x : A]) a) xs))
diff --git a/collects/typed-racket/base-env/prims.rkt b/collects/typed-racket/base-env/prims.rkt
index 3a61b1f5..1dc141a0 100644
--- a/collects/typed-racket/base-env/prims.rkt
+++ b/collects/typed-racket/base-env/prims.rkt
@@ -311,6 +311,8 @@ This file defines two sorts of primitives. All of them are provided into any mod
 (define-syntax (plambda: stx)
   (syntax-parse stx
     [(plambda: (tvars:id ...) formals . body)
+     #:fail-when (check-duplicate-identifier (syntax->list #'(tvars ...)))
+                 "duplicate type variable declaration"
      (quasisyntax/loc stx
        (#%expression
         #,(syntax-property (syntax/loc stx (lambda: formals . body))
@@ -320,6 +322,8 @@ This file defines two sorts of primitives. All of them are provided into any mod
 (define-syntax (pcase-lambda: stx)
   (syntax-parse stx
     [(pcase-lambda: (tvars:id ...) cl ...)
+     #:fail-when (check-duplicate-identifier (syntax->list #'(tvars ...)))
+                 "duplicate type variable declaration"
      (quasisyntax/loc stx
        (#%expression
         #,(syntax-property (syntax/loc stx (case-lambda: cl ...))
@@ -329,6 +333,8 @@ This file defines two sorts of primitives. All of them are provided into any mod
 (define-syntax (popt-lambda: stx)
   (syntax-parse stx
     [(popt-lambda: (tvars:id ...) formals . body)
+     #:fail-when (check-duplicate-identifier (syntax->list #'(tvars ...)))
+                 "duplicate type variable declaration"
      (quasisyntax/loc stx
        (#%expression
         #,(syntax-property (syntax/loc stx (opt-lambda: formals . body))
diff --git a/collects/typed-racket/private/parse-type.rkt b/collects/typed-racket/private/parse-type.rkt
index 036d5cb1..bb1326e2 100644
--- a/collects/typed-racket/private/parse-type.rkt
+++ b/collects/typed-racket/private/parse-type.rkt
@@ -51,6 +51,8 @@
   ;(printf "parse-all-type: ~a \n" (syntax->datum stx))
   (syntax-parse stx #:literals (t:All)
     [((~and kw t:All) (vars:id ... v:id dd:ddd) . t)
+     (when (check-duplicate-identifier (syntax->list #'(vars ... v)))
+       (tc-error "All: duplicate type variable or index"))
      (let* ([vars (map syntax-e (syntax->list #'(vars ...)))]
             [v (syntax-e #'v)])
        (add-disappeared-use #'kw)
@@ -58,6 +60,8 @@
          (extend-tvars vars
            (make-PolyDots (append vars (list v)) (parse-all-body #'t)))))]
     [((~and kw t:All) (vars:id ...) . t)
+     (when (check-duplicate-identifier (syntax->list #'(vars ...)))
+       (tc-error "All: duplicate type variable"))
      (let* ([vars (map syntax-e (syntax->list #'(vars ...)))])
        (add-disappeared-use #'kw)
        (extend-tvars vars