diff --git a/foreign/c/c-bytevectors.scm b/foreign/c/c-bytevectors.scm
index 31f380e..06fe660 100644
--- a/foreign/c/c-bytevectors.scm
+++ b/foreign/c/c-bytevectors.scm
@@ -458,10 +458,6 @@
                (racket (if (system-big-endian?) 'big 'little))
                (else 'big)))
 
-;;; Already defined by (scheme base):
-;;;
-;;;     c-bytevector? make-c-bytevector c-bytevector-length
-
 (define (c-bytevector=? bv1 bv2)
   (if (and (c-bytevector? bv1)
            (c-bytevector? bv2))
diff --git a/foreign/c/primitives/stklos.scm b/foreign/c/primitives/stklos.scm
index deb24a7..2d244d1 100644
--- a/foreign/c/primitives/stklos.scm
+++ b/foreign/c/primitives/stklos.scm
@@ -25,7 +25,8 @@
 
 (define c-bytevector?
   (lambda (object)
-    (cpointer? object)))
+    (and (not (void? object))
+         (cpointer? object))))
 
 (define-syntax define-c-procedure
   (syntax-rules ()