# UNDF: UNDF-2026-000000932
--- a/src/main/java/com/sparrowwallet/sparrow/wallet/UtxoEntry.java
+++ b/src/main/java/com/sparrowwallet/sparrow/wallet/UtxoEntry.java
@@ -149,16 +149,23 @@ public class UtxoEntry extends HashIndexEntry {

         public int recountMixesDone(Wallet postmixWallet, BlockTransactionHashIndex postmixUtxo) {
             int mixesDone = 0;
-            Set<BlockTransactionHashIndex> walletTxos = postmixWallet.getWalletTxos().entrySet().stream()
-                    .filter(entry -> entry.getValue().getKeyPurpose() == KeyPurpose.RECEIVE).map(Map.Entry::getKey).collect(Collectors.toSet());
+            // Build a lookup index: txHash -> set of output indices for O(1) membership test
+            // instead of streaming the entire walletTxos set per input per mix iteration
+            Map<Sha256Hash, Set<Long>> txoIndex = new HashMap<>();
+            for(Map.Entry<BlockTransactionHashIndex, WalletNode> entry : postmixWallet.getWalletTxos().entrySet()) {
+                if(entry.getValue().getKeyPurpose() == KeyPurpose.RECEIVE) {
+                    BlockTransactionHashIndex txo = entry.getKey();
+                    txoIndex.computeIfAbsent(txo.getHash(), k -> new HashSet<>()).add(txo.getIndex());
+                }
+            }
             BlockTransaction blkTx = postmixWallet.getTransactions().get(postmixUtxo.getHash());

             while(blkTx != null) {
                 mixesDone++;
                 List<TransactionInput> inputs = blkTx.getTransaction().getInputs();
                 blkTx = null;
                 for(TransactionInput txInput : inputs) {
                     BlockTransaction inputTx = postmixWallet.getTransactions().get(txInput.getOutpoint().getHash());
-                    if(inputTx != null && walletTxos.stream().anyMatch(txo -> txo.getHash().equals(inputTx.getHash()) && txo.getIndex() == txInput.getOutpoint().getIndex()) && inputTx.getTransaction() != null) {
+                    Set<Long> indices = inputTx == null ? null : txoIndex.get(inputTx.getHash());
+                    if(inputTx != null && indices != null && indices.contains(txInput.getOutpoint().getIndex()) && inputTx.getTransaction() != null) {
                         blkTx = inputTx;
                     }
                 }