diff --git a/node/src/main/kotlin/net/corda/node/services/persistence/DBTransactionStorage.kt b/node/src/main/kotlin/net/corda/node/services/persistence/DBTransactionStorage.kt
index 3b8246c47f..dcb171c820 100644
--- a/node/src/main/kotlin/net/corda/node/services/persistence/DBTransactionStorage.kt
+++ b/node/src/main/kotlin/net/corda/node/services/persistence/DBTransactionStorage.kt
@@ -101,8 +101,16 @@ class DBTransactionStorage(cacheSizeBytes: Long, private val database: CordaPers
 
     override fun addTransaction(transaction: SignedTransaction): Boolean = database.transaction {
         txStorage.concurrent {
-            addWithDuplicatesAllowed(transaction.id, transaction.toTxCacheValue()).apply {
-                updatesPublisher.bufferUntilDatabaseCommit().onNext(transaction)
+            // Be optimistic if we are a flow and never restarted (i.e. cannot have been to the flow hospital due to primary key collision).
+            val optimistic = FlowStateMachineImpl.currentStateMachine()?.isNotRestarted ?: false
+            if (optimistic) {
+                set(transaction.id, transaction.toTxCacheValue()).apply {
+                    updatesPublisher.bufferUntilDatabaseCommit().onNext(transaction)
+                }
+            } else {
+                addWithDuplicatesAllowed(transaction.id, transaction.toTxCacheValue()).apply {
+                    updatesPublisher.bufferUntilDatabaseCommit().onNext(transaction)
+                }
             }
         }
     }
diff --git a/node/src/main/kotlin/net/corda/node/services/statemachine/FlowStateMachineImpl.kt b/node/src/main/kotlin/net/corda/node/services/statemachine/FlowStateMachineImpl.kt
index a5d48cb57e..ba73c6eedf 100644
--- a/node/src/main/kotlin/net/corda/node/services/statemachine/FlowStateMachineImpl.kt
+++ b/node/src/main/kotlin/net/corda/node/services/statemachine/FlowStateMachineImpl.kt
@@ -87,6 +87,9 @@ class FlowStateMachineImpl<R>(override val id: StateMachineRunId,
     internal var transientValues: TransientReference<TransientValues>? = null
     internal var transientState: TransientReference<StateMachineState>? = null
 
+    // Utilise the behaviour of `ourSenderUUID` to indicate whether we have restarted ever.  Can be used to make certain code paths optimistic.
+    internal val isNotRestarted: Boolean get() = (ourSenderUUID != null)
+
     /**
      * What sender identifier to put on messages sent by this flow.  This will either be the identifier for the current
      * state machine manager / messaging client, or null to indicate this flow is restored from a checkpoint and