diff --git a/bitcoin/feerate.c b/bitcoin/feerate.c
index c6b37c17c..f02d45d64 100644
--- a/bitcoin/feerate.c
+++ b/bitcoin/feerate.c
@@ -39,12 +39,3 @@ const char *feerate_style_name(enum feerate_style style)
 	}
 	abort();
 }
-
-size_t common_weight(size_t num_inputs, size_t num_outputs)
-{
-	/*(nVersion + num inputs + num outputs + locktime) * 4
-	 *         + SegWit marker + SegWit flag */
-	return (4 + varint_size(num_inputs) +
-		varint_size(num_outputs) + 4) * 4
-		+ 1 + 1;
-}
diff --git a/bitcoin/feerate.h b/bitcoin/feerate.h
index 6190625aa..43bec2118 100644
--- a/bitcoin/feerate.h
+++ b/bitcoin/feerate.h
@@ -34,11 +34,6 @@
  */
 #define FEERATE_FLOOR 253
 
-/*
- * This is the net common weight of a transaction.
- */
-size_t common_weight(size_t num_inputs, size_t num_outputs);
-
 enum feerate_style {
 	FEERATE_PER_KSIPA,
 	FEERATE_PER_KBYTE
diff --git a/openingd/dualopend.c b/openingd/dualopend.c
index 132095b59..7ab9a4e1b 100644
--- a/openingd/dualopend.c
+++ b/openingd/dualopend.c
@@ -279,7 +279,8 @@ static bool check_balances(struct state *state,
 	if (check_opener_balance) {
 		u8 *funding_wscript;
 
-		weight = common_weight(psbt->num_inputs, psbt->num_outputs);
+		weight = bitcoin_tx_core_weight(psbt->num_inputs,
+						psbt->num_outputs);
 		funding_wscript = bitcoin_redeem_2of2(tmpctx,
 						      &state->our_funding_pubkey,
 						      &state->their_funding_pubkey);