diff --git a/Commands/building/CmdAbort.cs b/Commands/building/CmdAbort.cs
index 34182684c..d891978ac 100644
--- a/Commands/building/CmdAbort.cs
+++ b/Commands/building/CmdAbort.cs
@@ -39,7 +39,7 @@ namespace MCGalaxy.Commands.Building {
             p.DefaultBrushArgs = "";
             
             lock (p.level.queueLock)
-                p.level.blockqueue.RemoveAll(b => b.SessionID == p.SessionID);
+            	p.level.blockqueue.RemoveAll(b => (int)((b >> 9) & Player.SessionIDMask) == p.SessionID);
             Player.Message(p, "Every toggle or action was aborted.");
         }
         
diff --git a/Levels/BlockQueue.cs b/Levels/BlockQueue.cs
index 6dc21fac7..e0aabe66f 100644
--- a/Levels/BlockQueue.cs
+++ b/Levels/BlockQueue.cs
@@ -52,11 +52,18 @@ namespace MCGalaxy {
 
         public static void Addblock(Player p, int index, byte type, byte extType = 0) {
         	if (index == -1) return;
-            QueuedBlock item;
-            item.SessionID = p.SessionID; item.Index = index;
-            item.Type = type; item.ExtType = extType;
+        	// Bit packing format
+        	// 32-63: index
+        	// 9-31: session ID
+        	// 8: is ext block or not
+        	// 0-7: raw type
+        	ulong flags = (ulong)index << 32;
+        	flags |= (ulong)p.SessionID << 9;
+        	flags |= (type == Block.custom_block ? 0x100UL : 0x000UL);
+        	flags |= (type == Block.custom_block ? extType : type);
+        	
             lock (p.level.queueLock)
-                p.level.blockqueue.Add(item);
+                p.level.blockqueue.Add(flags);
         }
         
         static void ProcessLevelBlocks(Level lvl) {
@@ -67,9 +74,13 @@ namespace MCGalaxy {
                 if (lvl.blockqueue.Count < blockupdates || !lvl.HasPlayers())
                     count = lvl.blockqueue.Count;
 
-                for (int c = 0; c < count; c++) {
-                    QueuedBlock item = lvl.blockqueue[c];
-                    bulkSender.Add(item.Index, item.Type, item.ExtType);
+                for (int i = 0; i < count; i++) {
+                	ulong flags = lvl.blockqueue[i];
+                	int index = (int)(flags >> 32);                	
+                	byte type = (flags & 0x100) != 0 ? Block.custom_block : (byte)flags;
+                	byte extType = (flags & 0x100) != 0 ? (byte)flags : Block.air;
+                	
+                    bulkSender.Add(index, type, extType);
                     bulkSender.CheckIfSend(false);
                 }
                 bulkSender.CheckIfSend(true);
@@ -80,7 +91,5 @@ namespace MCGalaxy {
                 lvl.blockqueue.Clear();
             }
         }
-
-        public struct QueuedBlock { public int SessionID, Index; public byte Type, ExtType; }
     }
 }
diff --git a/Levels/Level.cs b/Levels/Level.cs
index a049cc4dd..8da3a22d4 100644
--- a/Levels/Level.cs
+++ b/Levels/Level.cs
@@ -235,7 +235,7 @@ namespace MCGalaxy
         
         public bool bufferblocks = Server.bufferblocks;
         internal readonly object queueLock = new object(), saveLock = new object(), savePropsLock = new object();
-        public List<BlockQueue.QueuedBlock> blockqueue = new List<BlockQueue.QueuedBlock>();
+        public List<ulong> blockqueue = new List<ulong>();
         readonly object physThreadLock = new object();
         BufferedBlockSender bulkSender;
 
diff --git a/Player/Player.Fields.cs b/Player/Player.Fields.cs
index c02a1f2a9..004d28fc8 100644
--- a/Player/Player.Fields.cs
+++ b/Player/Player.Fields.cs
@@ -183,6 +183,7 @@ namespace MCGalaxy {
         public bool voted = false;
         public bool flipHead = false;
         public GameProps Game = new GameProps();
+        public const int SessionIDMask = (1 << 23) - 1;
         public int SessionID;
 
         //Countdown
diff --git a/Player/Player.cs b/Player/Player.cs
index c36801e76..f07a6e123 100644
--- a/Player/Player.cs
+++ b/Player/Player.cs
@@ -65,14 +65,14 @@ namespace MCGalaxy {
             name = playername;
             truename = playername;
             DisplayName = playername;
-            SessionID = Interlocked.Increment(ref sessionCounter);
+            SessionID = Interlocked.Increment(ref sessionCounter) & SessionIDMask;
         }
 
         public Player(Socket s) {
             try {
                 socket = s;
                 ip = socket.RemoteEndPoint.ToString().Split(':')[0];
-                SessionID = Interlocked.Increment(ref sessionCounter);
+                SessionID = Interlocked.Increment(ref sessionCounter) & SessionIDMask;
                 Server.s.Log(ip + " connected to the server.");
 
                 for (byte i = 0; i < 128; i++) bindings[i] = i;