diff --git a/node/src/main/kotlin/net/corda/node/utilities/AppendOnlyPersistentMap.kt b/node/src/main/kotlin/net/corda/node/utilities/AppendOnlyPersistentMap.kt
index 4912871b46..c6b875dbd9 100644
--- a/node/src/main/kotlin/net/corda/node/utilities/AppendOnlyPersistentMap.kt
+++ b/node/src/main/kotlin/net/corda/node/utilities/AppendOnlyPersistentMap.kt
@@ -57,6 +57,7 @@ abstract class AppendOnlyPersistentMapBase<K, V, E, out EK>(
             // Depending on 'store' method, this may insert without checking key duplication or it may avoid inserting a duplicated key.
             val existingInDb = store(key, value)
             if (existingInDb != null) { // Always reuse an existing value from the storage of a duplicated key.
+                isUnique = false
                 Optional.of(existingInDb)
             } else {
                 Optional.of(value)
diff --git a/node/src/test/kotlin/net/corda/node/services/persistence/DBTransactionStorageTests.kt b/node/src/test/kotlin/net/corda/node/services/persistence/DBTransactionStorageTests.kt
index 5247788410..4c2ffc2843 100644
--- a/node/src/test/kotlin/net/corda/node/services/persistence/DBTransactionStorageTests.kt
+++ b/node/src/test/kotlin/net/corda/node/services/persistence/DBTransactionStorageTests.kt
@@ -172,9 +172,22 @@ class DBTransactionStorageTests {
         assertEquals(expected, actual)
     }
 
-    private fun newTransactionStorage() {
+    @Test
+    fun `duplicates are detected when transaction is evicted from cache`() {
+        newTransactionStorage(cacheSizeBytesOverride = 0)
+        val transaction = newTransaction()
         database.transaction {
-            transactionStorage = DBTransactionStorage(NodeConfiguration.defaultTransactionCacheSize)
+            val firstInserted = transactionStorage.addTransaction(transaction)
+            val secondInserted = transactionStorage.addTransaction(transaction)
+            require(firstInserted) { "We inserted a fresh transaction" }
+            require(!secondInserted) { "Second time should be redundant" }
+            println("$firstInserted $secondInserted")
+        }
+    }
+
+    private fun newTransactionStorage(cacheSizeBytesOverride: Long? = null) {
+        database.transaction {
+            transactionStorage = DBTransactionStorage(cacheSizeBytesOverride ?: NodeConfiguration.defaultTransactionCacheSize)
         }
     }