diff --git a/xenomorph/xenomorph/array.rkt b/xenomorph/xenomorph/array.rkt
index 7e87ac68..4a53f90f 100644
--- a/xenomorph/xenomorph/array.rkt
+++ b/xenomorph/xenomorph/array.rkt
@@ -32,7 +32,7 @@ https://github.com/mbutterick/restructure/blob/master/src/Array.coffee
                                       '_currentOffset 0
                                       '_length @len)
                              parent))
-      (define len (resolve-length @len #:parent parent))
+      (define len (resolve-length @len port #:parent parent))
       (cond
         [(or (not len) (eq? @length-type 'bytes))
          (define end-pos (cond
diff --git a/xenomorph/xenomorph/buffer.rkt b/xenomorph/xenomorph/buffer.rkt
index 0dec0391..f0eb9d9d 100644
--- a/xenomorph/xenomorph/buffer.rkt
+++ b/xenomorph/xenomorph/buffer.rkt
@@ -15,7 +15,7 @@ https://github.com/mbutterick/restructure/blob/master/src/Buffer.coffee
       (raise-argument-error '+xbuffer "resolvable length" @len))
 
     (define/augment (xxdecode port parent)
-      (define len (resolve-length @len #:parent parent))
+      (define len (resolve-length @len port #:parent parent))
       (read-bytes len))
 
     (define/augment (xxencode buf port [parent #f])
diff --git a/xenomorph/xenomorph/lazy-array.rkt b/xenomorph/xenomorph/lazy-array.rkt
index 23ebc5e6..3e92d67b 100644
--- a/xenomorph/xenomorph/lazy-array.rkt
+++ b/xenomorph/xenomorph/lazy-array.rkt
@@ -15,7 +15,7 @@ https://github.com/mbutterick/restructure/blob/master/src/LazyArray.coffee
 
     (define/override (xxdecode port parent)
       (define starting-pos (pos port)) ; ! placement matters. `resolve-length` will change `pos`
-      (define len (resolve-length @len #:parent parent))
+      (define len (resolve-length @len port #:parent parent))
       (define new-parent (if (xint? @len)
                              (mhasheq 'parent parent
                                       '_startOffset starting-pos
diff --git a/xenomorph/xenomorph/util.rkt b/xenomorph/xenomorph/util.rkt
index 8903f70f..e4df07ec 100644
--- a/xenomorph/xenomorph/util.rkt
+++ b/xenomorph/xenomorph/util.rkt
@@ -5,7 +5,7 @@
 (define (length-resolvable? x)
   (or (not x) (symbol? x) (xenomorphic? x) (procedure? x) (exact-nonnegative-integer? x)))
 
-(define (resolve-length x [port (current-input-port)] #:parent [parent #f])
+(define (resolve-length x port #:parent [parent #f])
   (cond
     [(not x) #f]
     [(exact-nonnegative-integer? x) x]