diff --git a/epan/addr_and_mask.c b/epan/addr_and_mask.c
index c730ba082a..d40e611643 100644
--- a/epan/addr_and_mask.c
+++ b/epan/addr_and_mask.c
@@ -56,7 +56,7 @@ tvb_get_ipv4_addr_with_prefix_len(tvbuff_t *tvb, int offset, ws_in4_addr *addr,
 	*addr = 0;
 	tvb_memcpy(tvb, addr, offset, addr_len);
 	if (prefix_len % 8)
-		addr[addr_len - 1] &= ((0xff00 >> (prefix_len % 8)) & 0xff);
+		((guint8*)addr)[addr_len - 1] &= ((0xff00 >> (prefix_len % 8)) & 0xff);
 	return addr_len;
 }