diff --git a/src/netbios_session.c b/src/netbios_session.c
index 25925b2..a56c0cc 100644
--- a/src/netbios_session.c
+++ b/src/netbios_session.c
@@ -246,7 +246,7 @@ int               netbios_session_packet_append(netbios_session *s,
     assert(s && s->packet);
 
     if (s->packet_payload_size - s->packet_cursor < size)
-        if (!session_buffer_realloc(s, size + s->packet_cursor))
+        if (!session_buffer_realloc(s, size + s->packet_cursor + sizeof(netbios_session_packet)))
             return 0;
 
     start = ((char *)&s->packet->payload) + s->packet_cursor;