diff --git a/net.c b/net.c
index 2117b6c5..a0bf7906 100644
--- a/net.c
+++ b/net.c
@@ -610,6 +610,20 @@ _order_transaction_id( coap_queue_t *lhs, coap_queue_t *rhs ) {
     : 1;
 }
 
+/** 
+ * Checks if @p opt fits into the message that ends with @p maxpos.
+ * This function returns @c 1 on success, or @c 0 if the option @p opt
+ * would exceed @p maxpos.
+ */
+static inline int
+check_opt_size(coap_opt_t *opt, unsigned char *maxpos) {
+  if (opt && opt < maxpos) {
+    if (((*opt & 0x0f) < 0x0f) || (opt + 1 < maxpos))
+      return opt + COAP_OPT_SIZE(opt) < maxpos;
+  }
+  return 0;
+}
+
 int
 coap_read( coap_context_t *ctx ) {
 #ifndef WITH_CONTIKI
@@ -707,6 +721,12 @@ coap_read( coap_context_t *ctx ) {
       } else {
 	--cnt;
       }
+
+      if (cnt &&
+	  !check_opt_size(opt, (unsigned char *)node->pdu->hdr + node->pdu->max_size)) {
+	debug("drop\n");
+	goto error;
+      }
       opt = options_next(opt);
     }
 
diff --git a/option.c b/option.c
index e2e306aa..7600d8ca 100644
--- a/option.c
+++ b/option.c
@@ -40,7 +40,7 @@ coap_option_iterator_init(coap_pdu_t *pdu, coap_opt_iterator_t *oi,
 }
 
 #define IS_EMPTY_NOOP(Type,Option) \
-  ((Type) % COAP_OPTION_NOOP == 0 && COAP_OPT_LENGTH(Option) == 0)
+  (((Type) % COAP_OPTION_NOOP == 0) && (COAP_OPT_LENGTH(Option) == 0))
 
 #define opt_finished(oi) ((oi)->optcnt == COAP_OPT_LONG			\
 			  ? ((oi)->option && *((oi)->option) == COAP_OPT_END) \
@@ -56,24 +56,25 @@ coap_option_next(coap_opt_iterator_t *oi) {
   /* proceed to next option */
   if (oi->n++) {
     oi->option = options_next(oi->option);
+    if (opt_finished(oi))
+      return NULL;
     oi->type += COAP_OPT_DELTA(oi->option);
   }
   
   /* Skip subsequent options if it is an empty no-op (used for
    * fence-posting) or the filter bit is not set. */
-  while (!opt_finished(oi) && 
-	 (IS_EMPTY_NOOP(oi->type, oi->option)
-	  || coap_option_getb(oi->filter, oi->type) == 0)) {
+  while (oi->option && (IS_EMPTY_NOOP(oi->type, oi->option)
+			|| coap_option_getb(oi->filter, oi->type) == 0)) {
     oi->n++;
     oi->option = options_next(oi->option);
 
-    if (opt_finished(oi))
-      break;
+    if (!oi->option || opt_finished(oi))
+      return NULL;
 
     oi->type += COAP_OPT_DELTA(oi->option);
   }
   
-  return opt_finished(oi) ? NULL : oi->option;
+  return oi->option;
 }
 
 coap_opt_t *