diff --git a/racket/src/cs/rumble/check.ss b/racket/src/cs/rumble/check.ss
index c059ce4c10..3ed5927035 100644
--- a/racket/src/cs/rumble/check.ss
+++ b/racket/src/cs/rumble/check.ss
@@ -53,7 +53,7 @@
   (unless (fx<= (fx+ d-start s-len) d-len)
     (raise-arguments-error who (string-append "not enough room in target " what)
                            "target length" d-len
-                           "needed length" s-len)))
+                           "needed length" (fx+ d-start s-len))))
 
 (define (check-range who what in-value start end len)
   (unless (<= start len)
diff --git a/racket/src/cs/rumble/vector.ss b/racket/src/cs/rumble/vector.ss
index f9be7f3ac9..078c783bd0 100644
--- a/racket/src/cs/rumble/vector.ss
+++ b/racket/src/cs/rumble/vector.ss
@@ -287,7 +287,7 @@
   (case-lambda
    [(dest d-start src)
     (vector-copy! dest d-start src 0 (and (vector? src) (vector-length src)))]
-   [(src s-start dest d-start)
+   [(dest d-start src s-start)
     (vector-copy! dest d-start src s-start (and (vector? src) (vector-length src)))]
    [(dest d-start src s-start s-end)
     (check who mutable-vector? :contract "(and/c vector? (not/c immutable?))" dest)