diff --git a/src/packet.c b/src/packet.c
index 639368d..1b0eb39 100644
--- a/src/packet.c
+++ b/src/packet.c
@@ -466,7 +466,7 @@ Buffer *encode_suback(SubAckPayload *payload) {
 
 Buffer *encode_unsubscribe(UnsubscribePayload *payload) {
     size_t sz = 2; // packet id
-    sz += strlen(payload->topic); // topic
+    sz += strlen(payload->topic) + 2; // topic
 
     Buffer *buffer = make_buffer_for_header(sz, PacketTypeUnsubscribe);