diff --git a/src/main/scala/com/fluency03/blockchain/core/Blockchain.scala b/src/main/scala/com/fluency03/blockchain/core/Blockchain.scala
index 1e1481d..dd0c9b5 100644
--- a/src/main/scala/com/fluency03/blockchain/core/Blockchain.scala
+++ b/src/main/scala/com/fluency03/blockchain/core/Blockchain.scala
@@ -56,7 +56,9 @@ object Blockchain {
     ): Map[Outpoint, TxOut] = {
       val newUnspentTxOuts = getNewUTxOs(transactions)
       val consumedTxOuts = getConsumedUTxOs(transactions)
-      unspentTxOuts.filterKeys(consumedTxOuts contains) ++ newUnspentTxOuts
+      unspentTxOuts.filterNot {
+        case (i, _) => consumedTxOuts.contains(i)
+      } ++ newUnspentTxOuts
     }
 
   def getNewUTxOs(transactions: Seq[Transaction]): Map[Outpoint, TxOut] =
diff --git a/src/test/scala/com/fluency03/blockchain/core/BlockchainTest.scala b/src/test/scala/com/fluency03/blockchain/core/BlockchainTest.scala
index bcd96f0..3eff4e5 100644
--- a/src/test/scala/com/fluency03/blockchain/core/BlockchainTest.scala
+++ b/src/test/scala/com/fluency03/blockchain/core/BlockchainTest.scala
@@ -1,6 +1,6 @@
 package com.fluency03.blockchain
 package core
-
+import com.fluency03.blockchain.core.Blockchain.updateUTxOs
 import com.fluency03.blockchain.core.Transaction.createCoinbaseTx
 import org.json4s.JValue
 import org.json4s.native.JsonMethods.parse
@@ -59,9 +59,22 @@ class BlockchainTest extends FlatSpec with Matchers  {
   }
 
   "updateUTxOs" should "update the UTXOs from a latest Seq of transactions." in {
-
-
-
+    val tx: Transaction = Transaction(
+      Seq(TxIn(Outpoint("def0", 0), "abc1"),
+        TxIn(Outpoint("def0", 1), "abc1")),
+      Seq(TxOut("abc4", 40)),
+      genesisTimestamp
+    )
+
+    val unspentTxOuts1: mutable.Map[Outpoint, TxOut] = mutable.Map.empty[Outpoint, TxOut]
+    unspentTxOuts1 += (Outpoint("def0", 0) -> TxOut("abc4", 20))
+    unspentTxOuts1 += (Outpoint("def0", 1) -> TxOut("abc4", 20))
+
+    val unspentTxOuts2: mutable.Map[Outpoint, TxOut] = mutable.Map.empty[Outpoint, TxOut]
+    updateUTxOs(Seq(tx), unspentTxOuts1.toMap) should not equal unspentTxOuts2
+
+    unspentTxOuts2 += (Outpoint(tx.id, 0) -> TxOut("abc4", 40))
+    updateUTxOs(Seq(tx), unspentTxOuts1.toMap) shouldEqual unspentTxOuts2
   }