diff --git a/src/dns.c b/src/dns.c
index fd3ce25..bd1257f 100644
--- a/src/dns.c
+++ b/src/dns.c
@@ -45,7 +45,7 @@
 
 int dnsc_use_edns0 = 1;
 
-#define CHECKLEN(x) if (buflen - (p-buf) < (x))  return 0
+#define CHECKLEN(x) if (buflen < (x) + (unsigned)(p-buf))  return 0
 
 int
 dns_encode(char *buf, size_t buflen, struct query *q, qr_t qr, char *data, size_t datalen)
@@ -391,7 +391,7 @@ dns_get_id(char *packet, size_t packetlen)
 	return ntohs(header->id);
 }
 
-#define CHECKLEN(x) if (packetlen - (data-packet) < (x))  return 0
+#define CHECKLEN(x) if (packetlen < (x) + (unsigned)(data-packet))  return 0
 
 int
 dns_decode(char *buf, size_t buflen, struct query *q, qr_t qr, char *packet, size_t packetlen)