diff --git a/collects/tests/typed-racket/unit-tests/typecheck-tests.rkt b/collects/tests/typed-racket/unit-tests/typecheck-tests.rkt
index a462f91c..1974ce03 100644
--- a/collects/tests/typed-racket/unit-tests/typecheck-tests.rkt
+++ b/collects/tests/typed-racket/unit-tests/typecheck-tests.rkt
@@ -368,7 +368,7 @@
         [tc-e (string-join '("hello" "world") #:before-first "a") -String]
         [tc-e (add-between '(1 2 3) 0) (-lst -Byte)]
         [tc-e (add-between '(1 2 3) 'a) (-lst (t:Un -PosByte (-val 'a)))]
-        [tc-e ((inst add-between Positive-Byte Symbol) '(1 2 3) 'a #:before-first 'b) (-lst (t:Un -PosByte -Symbol))]
+        [tc-e ((inst add-between Positive-Byte Symbol) '(1 2 3) 'a #:splice? #t #:before-first '(b)) (-lst (t:Un -PosByte -Symbol))]
 
         [tc-e (apply (plambda: (a) [x : a *] x) '(5)) (-lst -PosByte)]
         [tc-e (apply append (list '(1 2 3) '(4 5 6))) (-lst -PosByte)]
diff --git a/collects/typed-racket/base-env/base-env.rkt b/collects/typed-racket/base-env/base-env.rkt
index 71839841..38591b3b 100644
--- a/collects/typed-racket/base-env/base-env.rkt
+++ b/collects/typed-racket/base-env/base-env.rkt
@@ -1426,10 +1426,9 @@
 [last   (-poly (a) ((-lst a) . -> . a))]
 [add-between (-poly (a b) ((-lst a) b
                            #:splice? -Boolean #f
-                           #:nothing Univ #f ; default is gensym
-                           #:before-first b #f
+                           #:before-first (-lst b) #f
                            #:before-last b #f
-                           #:after-last b #f
+                           #:after-last (-lst b) #f
                            . ->key . (-lst (Un a b))))]
 
 [last-pair (-poly (a) ((-mu x (Un a (-val '()) (-pair a x)))