diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java b/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
index 54f4463..a9f8154 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/PushOne.java
@@ -122,7 +122,7 @@
 
   private final Project.NameKey projectName;
   private final URIish uri;
-  private final Set<ImmutableSet<String>> refBatchesToPush = Sets.newHashSetWithExpectedSize(4);
+  private final Set<ImmutableSet<String>> refBatchesToPush = Sets.newConcurrentHashSet();
   private boolean pushAllRefs;
   private Repository git;
   private boolean isCollision;