diff --git a/bag_replicator/src/test/scala/weco/storage_service/bag_replicator/replicator/ReplicatorTestCases.scala b/bag_replicator/src/test/scala/weco/storage_service/bag_replicator/replicator/ReplicatorTestCases.scala
index cd427eb69..92aaa6792 100644
--- a/bag_replicator/src/test/scala/weco/storage_service/bag_replicator/replicator/ReplicatorTestCases.scala
+++ b/bag_replicator/src/test/scala/weco/storage_service/bag_replicator/replicator/ReplicatorTestCases.scala
@@ -312,7 +312,7 @@ trait ReplicatorTestCases[
         val dstPrefix = createDstPrefixWith(dstNamespace)
 
         withPrefixTransfer { prefixTransfer =>
-          val spyTransfer = spy(prefixTransfer)
+          val spyTransfer = spy[PrefixTransferImpl](prefixTransfer)
 
           withReplicator(spyTransfer) {
             _.replicate(