diff --git a/packages/stack/src/blockchain/blockchain-inmemory.ts b/packages/stack/src/blockchain/blockchain-inmemory.ts
index 4fb5111..9d39a21 100644
--- a/packages/stack/src/blockchain/blockchain-inmemory.ts
+++ b/packages/stack/src/blockchain/blockchain-inmemory.ts
@@ -156,11 +156,19 @@ export class BlockchainInMemory extends BaseBlockchain<BlockHeightPayload> {
       );
     }
 
+    // Check if the transaction has a mempool input, if there is one, we need to set the height to -1 to indicate that it uses an unconfirmed input
+    const hasMempoolInput = tx.getInputs().some((input) => {
+      const tx = this.transactions.get(binToHex(input.outpointTransactionHash));
+      if (!tx) return false;
+
+      return tx.height <= 0;
+    });
+
     // Add the transaction.
     this.addTransaction({
       hash: tx.toHash(),
       transaction: tx,
-      height: 0,
+      height: hasMempoolInput ? -1 : 0,
     });
 
     // Notify our address and transaction subscribers.
@@ -330,10 +338,11 @@ export class BlockchainInMemory extends BaseBlockchain<BlockHeightPayload> {
     for (const tx of this.transactions.values()) {
       tx.transaction.getOutputs().forEach((output, outpointIndex) => {
         const utxo: BlockchainUTXO = {
-          height: 0,
+          height: tx.height,
           utxo: UTXO.from(new Outpoint(tx.hash.toBytes(), outpointIndex), {
             valueSatoshis: output.valueSatoshis,
             lockingBytecode: output.lockingBytecode,
+            token: output.token,
           }),
         };
         utxoMap.set(`${tx.hash.toHex()}:${outpointIndex}`, utxo);