diff --git a/lightningd/commit_tx.c b/lightningd/commit_tx.c
index 7f8358466..5cf5dde2c 100644
--- a/lightningd/commit_tx.c
+++ b/lightningd/commit_tx.c
@@ -232,7 +232,9 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 	tx = bitcoin_tx(ctx, 1, untrimmed + 2);
 
 	/* We keep track of which outputs have which HTLCs */
-	*htlcmap = tal_arr(tx, const struct htlc *, tal_count(tx->output));
+	if (htlcmap)
+		*htlcmap = tal_arr(tx, const struct htlc *,
+				   tal_count(tx->output));
 
 	/* This could be done in a single loop, but we follow the BOLT
 	 * literally to make comments in test vectors clearer. */
@@ -249,7 +251,8 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 		if (trim(htlcs[i], feerate_per_kw, dust_limit_satoshis, side))
 			continue;
 		add_offered_htlc_out(tx, n, htlcs[i], selfkey, otherkey);
-		(*htlcmap)[n++] = htlcs[i];
+		if (htlcmap)
+			(*htlcmap)[n++] = htlcs[i];
 	}
 
 	/* BOLT #3:
@@ -263,7 +266,8 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 		if (trim(htlcs[i], feerate_per_kw, dust_limit_satoshis, side))
 			continue;
 		add_received_htlc_out(tx, n, htlcs[i],selfkey, otherkey);
-		(*htlcmap)[n++] = htlcs[i];
+		if (htlcmap)
+			(*htlcmap)[n++] = htlcs[i];
 	}
 
 	/* BOLT #3:
@@ -279,7 +283,8 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 						       self_delayedkey);
 		tx->output[n].amount = self_pay_msat / 1000;
 		tx->output[n].script = scriptpubkey_p2wsh(tx, wscript);
-		(*htlcmap)[n] = NULL;
+		if (htlcmap)
+			(*htlcmap)[n] = NULL;
 		SUPERVERBOSE("# to-local amount %"PRIu64" wscript %s\n",
 			     tx->output[n].amount,
 			     tal_hex(tmpctx, wscript));
@@ -302,7 +307,8 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 		 */
 		tx->output[n].amount = other_pay_msat / 1000;
 		tx->output[n].script = scriptpubkey_p2wpkh(tx, otherkey);
-		(*htlcmap)[n] = NULL;
+		if (htlcmap)
+			(*htlcmap)[n] = NULL;
 		SUPERVERBOSE("# to-remote amount %"PRIu64" P2WPKH(%s)\n",
 			     tx->output[n].amount,
 			     type_to_string(tmpctx, struct pubkey, otherkey));
@@ -311,7 +317,8 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 
 	assert(n <= tal_count(tx->output));
 	tal_resize(&tx->output, n);
-	tal_resize(htlcmap, n);
+	if (htlcmap)
+		tal_resize(htlcmap, n);
 
 	/* BOLT #3:
 	 *
@@ -319,7 +326,7 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 	 *    order](#transaction-input-and-output-ordering)
 	 */
 	permute_outputs(tx->output, tal_count(tx->output),
-			(const void **)*htlcmap);
+			htlcmap ? (const void **)*htlcmap : NULL);
 
 	/* BOLT #3:
 	 *
diff --git a/lightningd/commit_tx.h b/lightningd/commit_tx.h
index 2473c1db8..1e874264e 100644
--- a/lightningd/commit_tx.h
+++ b/lightningd/commit_tx.h
@@ -51,7 +51,7 @@ u64 commit_tx_base_fee(u64 feerate_per_kw, size_t num_untrimmed_htlcs);
  * @self_pay_msat: amount to pay directly to self
  * @other_pay_msat: amount to pay directly to the other side
  * @htlcs: tal_arr of htlcs committed by transaction (some may be trimmed)
- * @htlc_map: outputed map of outnum->HTLC (NULL for direct outputs).
+ * @htlc_map: outputed map of outnum->HTLC (NULL for direct outputs), or NULL.
  * @obscured_commitment_number: number to encode in commitment transaction
  * @side: side to generate commitment transaction for.
  *