diff --git a/node-api/src/main/kotlin/net/corda/nodeapi/internal/serialization/kryo/CustomSerializerCheckpointAdaptor.kt b/node-api/src/main/kotlin/net/corda/nodeapi/internal/serialization/kryo/CustomSerializerCheckpointAdaptor.kt
index 4cc41110c6..4f3475696b 100644
--- a/node-api/src/main/kotlin/net/corda/nodeapi/internal/serialization/kryo/CustomSerializerCheckpointAdaptor.kt
+++ b/node-api/src/main/kotlin/net/corda/nodeapi/internal/serialization/kryo/CustomSerializerCheckpointAdaptor.kt
@@ -13,7 +13,7 @@ import kotlin.reflect.jvm.jvmErasure
 /**
  * Adapts CheckpointCustomSerializer for use in Kryo
  */
-class CustomSerializerCheckpointAdaptor<OBJ, PROXY>(private val userSerializer : CheckpointCustomSerializer<OBJ, PROXY>) : Serializer<OBJ>() {
+internal class CustomSerializerCheckpointAdaptor<OBJ, PROXY>(private val userSerializer : CheckpointCustomSerializer<OBJ, PROXY>) : Serializer<OBJ>() {
 
     /**
      * The class name of the serializer we are adapting.