diff --git a/bytevector-tests.scm b/bytevector-tests.scm
index c1e7bffb..afc7b20b 100644
--- a/bytevector-tests.scm
+++ b/bytevector-tests.scm
@@ -18,6 +18,10 @@
     bv)
 ) ;=⇒ #u8(1 3 3 4)
 
-(define a #u8(1 2 3 4 5))
-(write (Cyc-bytevector-copy a 2 4)) ; =⇒ #u8(3 4)
-
+;; TODO: does not work properly at the top-level
+(let ((x 1))
+  (define a #u8(1 2 3 4 5))
+  (define b #(1 2 3 4 5))
+  (write (Cyc-bytevector-copy a 2 4)) ; =⇒ #u8(3 4)
+  (write b)
+)