diff --git a/ares/ares_ipv6.h b/ares/ares_ipv6.h
index 28bc5ee27..3a5bd0699 100644
--- a/ares/ares_ipv6.h
+++ b/ares/ares_ipv6.h
@@ -29,8 +29,13 @@ struct in6_addr
 #endif
 
 #ifndef NS_IN6ADDRSZ
+#if SIZEOF_STRUCT_IN6_ADDR == 0
+/* We cannot have it set to zero, so we pick a fixed value here */
+#define NS_IN6ADDRSZ 16
+#else
 #define NS_IN6ADDRSZ SIZEOF_STRUCT_IN6_ADDR
 #endif
+#endif
 
 #ifndef NS_INADDRSZ
 #define NS_INADDRSZ SIZEOF_STRUCT_IN_ADDR