diff --git a/node/src/main/kotlin/net/corda/node/services/events/NodeSchedulerService.kt b/node/src/main/kotlin/net/corda/node/services/events/NodeSchedulerService.kt
index ff341af5d2..f13d1d73bf 100644
--- a/node/src/main/kotlin/net/corda/node/services/events/NodeSchedulerService.kt
+++ b/node/src/main/kotlin/net/corda/node/services/events/NodeSchedulerService.kt
@@ -32,7 +32,6 @@ import net.corda.nodeapi.internal.persistence.CordaPersistence
 import net.corda.nodeapi.internal.persistence.NODE_DATABASE_PREFIX
 import net.corda.nodeapi.internal.persistence.contextTransaction
 import org.apache.activemq.artemis.utils.ReusableLatch
-import org.apache.mina.util.ConcurrentHashSet
 import org.slf4j.Logger
 import java.time.Duration
 import java.time.Instant
@@ -147,7 +146,7 @@ class NodeSchedulerService(private val clock: CordaClock,
 
     // Used to de-duplicate flow starts in case a flow is starting but the corresponding entry hasn't been removed yet
     // from the database
-    private val startingStateRefs = ConcurrentHashSet<ScheduledStateRef>()
+    private val startingStateRefs: MutableSet<ScheduledStateRef> = ConcurrentHashMap.newKeySet<ScheduledStateRef>()
     private val mutex = ThreadBox(InnerState())
     private val schedulerTimerExecutor = Executors.newSingleThreadExecutor()