diff --git a/lib/isc/include/isc/radix.h b/lib/isc/include/isc/radix.h
index 24c183f2c2..ed6de39985 100644
--- a/lib/isc/include/isc/radix.h
+++ b/lib/isc/include/isc/radix.h
@@ -34,8 +34,9 @@
 
 #define NETADDR_TO_PREFIX_T(na,pt,bits,is_ecs)	\
 	do { \
+		const void *p = na; \
 		memset(&(pt), 0, sizeof(pt)); \
-		if((na) != NULL) { \
+		if (p != NULL) { \
 			(pt).family = (na)->family; \
 			(pt).bitlen = (bits); \
 			if ((pt).family == AF_INET6) { \