diff --git a/lib/scheme/extras.scm b/lib/scheme/extras.scm
index 9796a0e1..a9279464 100644
--- a/lib/scheme/extras.scm
+++ b/lib/scheme/extras.scm
@@ -134,9 +134,9 @@
 (define (read-bytevector n . o)
   (if (zero? n)
       #u8()
-      (let ((in (if (pair? o) (car o) (current-input-port)))
-            (vec (make-bytevector n))
-            (res (read-bytevector! vec in)))
+      (let* ((in (if (pair? o) (car o) (current-input-port)))
+             (vec (make-bytevector n))
+             (res (read-bytevector! vec in)))
         (cond ((eof-object? res) res)
               ((< res n) (subbytes vec 0 i))
               (else res)))))