diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c
index 0fddc17106bd..5b71a289d04f 100644
--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -275,7 +275,7 @@ batadv_frag_merge_packets(struct hlist_head *chain)
 	kfree(entry);
 
 	packet = (struct batadv_frag_packet *)skb_out->data;
-	size = ntohs(packet->total_size);
+	size = ntohs(packet->total_size) + hdr_size;
 
 	/* Make room for the rest of the fragments. */
 	if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {