diff --git a/apps/rest-coap/coap-common.c b/apps/rest-coap/coap-common.c
index 0a23fa0c5..deb4e222e 100644
--- a/apps/rest-coap/coap-common.c
+++ b/apps/rest-coap/coap-common.c
@@ -101,7 +101,7 @@ int serialize_packet(coap_packet_t* packet, uint8_t* buffer)
 
     memcpy((char*)&buffer[index], option->value, option->len);
     index += option->len;
-    option_delta += option->option;
+    option_delta = option->option;
   }
 
   if(packet->payload){