diff --git a/onchaind/onchaind.c b/onchaind/onchaind.c
index c33c598ef..e24f584fd 100644
--- a/onchaind/onchaind.c
+++ b/onchaind/onchaind.c
@@ -332,6 +332,7 @@ static struct bitcoin_tx *tx_to_us(const tal_t *ctx,
 
 	/* Worst-case sig is 73 bytes */
 	weight = bitcoin_tx_weight(tx) + 1 + 3 + 73 + 0 + tal_count(wscript);
+	weight = elements_add_overhead(weight, 1, 1);
 	fee = amount_tx_fee(feerate_per_kw, weight);
 
 	/* Result is trivial?  Spend with small feerate, but don't wait