diff --git a/src/main/java/moe/nekojimi/friendcloud/objects/Peer.java b/src/main/java/moe/nekojimi/friendcloud/objects/Peer.java
index 5702683..90ee40a 100644
--- a/src/main/java/moe/nekojimi/friendcloud/objects/Peer.java
+++ b/src/main/java/moe/nekojimi/friendcloud/objects/Peer.java
@@ -1,5 +1,6 @@
 package moe.nekojimi.friendcloud.objects;
 
+import moe.nekojimi.friendcloud.Util;
 import moe.nekojimi.friendcloud.protos.ObjectStatements;
 
 import java.net.URI;
@@ -13,6 +14,8 @@ public class Peer extends NetworkObject
     private String userName = "";
     private String systemName = "";
 
+	private long lastKnownChangeID = 0L;
+
     public Peer(ObjectID objectID)
     {
         super(objectID);
@@ -71,6 +74,7 @@ public class Peer extends NetworkObject
 		ret.put("userName", userName);
 		ret.put("systemName", systemName);
 		ret.put("addresses", addresses);
+		ret.put("lastKnownChangeID", lastKnownChangeID);
 		return ret;
 	}
 
@@ -81,6 +85,7 @@ public class Peer extends NetworkObject
 		systemName = map.get("systemName").toString();
 		addresses.clear();
 		addresses.addAll((Collection<? extends URI>) map.get("addresses"));
+		lastKnownChangeID = Util.unconditionalNumberToLong(map.getOrDefault("lastKnownChangeID", 0L));
 	}
 
 	public void addAddress(URI address)
@@ -129,6 +134,16 @@ public class Peer extends NetworkObject
 		this.systemName = systemName;
 	}
 
+	public long getLastKnownChangeID()
+	{
+		return lastKnownChangeID;
+	}
+
+	public void setLastKnownChangeID(long lastKnownChangeID)
+	{
+		this.lastKnownChangeID = lastKnownChangeID;
+	}
+
 	@Override
 	public String getFriendlyName()
 	{