diff --git a/collects/2htdp/private/image-more.ss b/collects/2htdp/private/image-more.ss
index 4af533fb28..291d358e6f 100644
--- a/collects/2htdp/private/image-more.ss
+++ b/collects/2htdp/private/image-more.ss
@@ -117,7 +117,7 @@
   (overlay/internal 'middle 'middle image (cons image2 image3)))
 
 ;; underlay : image image image ... -> image
-(define (underlay image image2 . image3)
+(define/chk (underlay image image2 . image3)
   (let ([imgs (reverse (list* image image2 image3))])
     (overlay/internal 'middle 'middle (car imgs) (cdr imgs))))
 
diff --git a/collects/2htdp/private/img-err.ss b/collects/2htdp/private/img-err.ss
index 2b072c8ac7..78ed2ca40e 100644
--- a/collects/2htdp/private/img-err.ss
+++ b/collects/2htdp/private/img-err.ss
@@ -49,7 +49,7 @@
       [(define/chk (fn-name args ... . final-arg) body ...)
        (identifier? #'final-arg)
        (let ([len (length (syntax->list #'(args ...)))])
-         (with-syntax ([(i ...) (build-list len values)])
+         (with-syntax ([(i ...) (build-list len add1)])
            #`(define (fn-name args ... . final-arg)
                (let ([args (check/normalize 'fn-name 'args args i)] ...
                      [final-arg (map/i (λ (x j) (check/normalize 'fn-name 'final-arg x (+ #,len j)))