diff --git a/typed-racket-lib/typed-racket/private/parse-type.rkt b/typed-racket-lib/typed-racket/private/parse-type.rkt
index 913e3970..44ca5fdf 100644
--- a/typed-racket-lib/typed-racket/private/parse-type.rkt
+++ b/typed-racket-lib/typed-racket/private/parse-type.rkt
@@ -689,10 +689,10 @@
   (define merged-augments (merge-clause super-augments augments))
 
   ;; make sure augments and methods are disjoint
-  (define maybe-dup-method (check-duplicate (dict-keys merged-methods)))
+  (define maybe-dup-method (check-duplicates (dict-keys merged-methods)))
   (when maybe-dup-method
     (parse-error "duplicate method name" "name" maybe-dup-method))
-  (define maybe-dup-augment (check-duplicate (dict-keys merged-augments)))
+  (define maybe-dup-augment (check-duplicates (dict-keys merged-augments)))
   (when maybe-dup-augment
     (parse-error "duplicate augmentable method name"
                  "name" maybe-dup-augment))
diff --git a/typed-racket-lib/typed-racket/private/type-contract.rkt b/typed-racket-lib/typed-racket/private/type-contract.rkt
index e76f3deb..1609ae74 100644
--- a/typed-racket-lib/typed-racket/private/type-contract.rkt
+++ b/typed-racket-lib/typed-racket/private/type-contract.rkt
@@ -642,7 +642,7 @@
          (for/list ([t arrs])
            (match t
              [(arr: dom _ _ _ _) (length dom)])))
-       (define maybe-dup (check-duplicate arities))
+       (define maybe-dup (check-duplicates arities))
        (when maybe-dup
          (fail #:reason (~a "function type has two cases of arity " maybe-dup)))
        (if (= (length arrs) 1)
diff --git a/typed-racket-lib/typed-racket/types/classes.rkt b/typed-racket-lib/typed-racket/types/classes.rkt
index 6570f3da..e0f0fa8a 100644
--- a/typed-racket-lib/typed-racket/types/classes.rkt
+++ b/typed-racket-lib/typed-racket/types/classes.rkt
@@ -60,14 +60,14 @@
             #:attr all-init-names (append (attribute init-field-names)
                                           (attribute init-names))
             #:fail-when
-            (check-duplicate (attribute all-init-names))
+            (check-duplicates (attribute all-init-names))
             "duplicate init or init-field clause"
             #:fail-when
-            (check-duplicate (attribute all-field-names))
+            (check-duplicates (attribute all-field-names))
             "duplicate field or init-field clause"
             #:fail-when
-            (check-duplicate (append (attribute method-names)
-                                     (attribute augment-names)))
+            (check-duplicates (append (attribute method-names)
+                                      (attribute augment-names)))
             "duplicate method or augmentable method clause"
             #:attr constraints
             (list (attribute all-init-names)
@@ -115,14 +115,14 @@
                                 (attribute augments)
                                 (attribute init-rest))
            #:fail-when
-           (check-duplicate (map first (attribute inits)))
+           (check-duplicates (map first (attribute inits)))
            "duplicate init or init-field clause"
            #:fail-when
-           (check-duplicate (map first (attribute fields)))
+           (check-duplicates (map first (attribute fields)))
            "duplicate field or init-field clause"
            #:fail-when
-           (check-duplicate (map first (append (attribute methods)
-                                               (attribute augments))))
+           (check-duplicates (map first (append (attribute methods)
+                                                (attribute augments))))
            "duplicate method or augmentable method clause"))
 
 ;; Type -> RowConstraint
@@ -228,16 +228,16 @@
                                  (parse-type (attribute init-rest-type)))
            #:with implements #'(implements-id ...)
            #:fail-when
-           (check-duplicate (map first (attribute inits)))
+           (check-duplicates (map first (attribute inits)))
            "duplicate init or init-field clause"
            #:fail-when
-           (check-duplicate (map first (attribute fields)))
+           (check-duplicates (map first (attribute fields)))
            "duplicate field or init-field clause"
            #:fail-when
-           (check-duplicate (map first (attribute methods)))
+           (check-duplicates (map first (attribute methods)))
            "duplicate method clause"
            #:fail-when
-           (check-duplicate (map first (attribute augments)))
+           (check-duplicates (map first (attribute augments)))
            "duplicate augment clause"))
 
 ;; Stx Stx Listof<Boolean> (Stx -> Type) -> Listof<(List Symbol Type Boolean)>
diff --git a/typed-racket-test/unit-tests/tooltip-tests.rkt b/typed-racket-test/unit-tests/tooltip-tests.rkt
index 17a845f7..9da37ba2 100644
--- a/typed-racket-test/unit-tests/tooltip-tests.rkt
+++ b/typed-racket-test/unit-tests/tooltip-tests.rkt
@@ -85,7 +85,7 @@
     (for/list ([tooltip (in-list tooltips)])
       (match-define (vector _ start end _) tooltip)
       (list start end)))
-  (if (check-duplicate locations)
+  (if (check-duplicates locations)
       'duplicate-tooltips
       #t))