diff --git a/sys/sys/bitops.h b/sys/sys/bitops.h
index 2aeeeec9dcff..b80fdc247214 100644
--- a/sys/sys/bitops.h
+++ b/sys/sys/bitops.h
@@ -1,4 +1,4 @@
-/*	$NetBSD: bitops.h,v 1.14 2018/03/08 20:32:32 christos Exp $	*/
+/*	$NetBSD: bitops.h,v 1.15 2021/09/12 15:22:05 rillig Exp $	*/
 
 /*-
  * Copyright (c) 2007, 2010 The NetBSD Foundation, Inc.
@@ -321,7 +321,7 @@ fast_remainder32(uint32_t _v, uint32_t _div, uint32_t _m, uint8_t _s1,
 #else
 #define __BITMAP_ZERO(__v) do {						\
 	size_t __i;							\
-	for (__i = 0; __i < __arraycount(__v->_b); __i++)		\
+	for (__i = 0; __i < __arraycount((__v)->_b); __i++)		\
 		(__v)->_b[__i] = 0;					\
 	} while (/* CONSTCOND */ 0)
 #endif /* GCC 2.95 */