diff --git a/src/main/java/com/anatawa12/fixRtm/ThreadUtil.kt b/src/main/java/com/anatawa12/fixRtm/ThreadUtil.kt
new file mode 100644
index 00000000..febbaa4a
--- /dev/null
+++ b/src/main/java/com/anatawa12/fixRtm/ThreadUtil.kt
@@ -0,0 +1,28 @@
+package com.anatawa12.fixRtm
+
+import net.minecraftforge.fml.common.eventhandler.SubscribeEvent
+import net.minecraftforge.fml.common.gameevent.TickEvent
+import java.util.concurrent.ConcurrentLinkedQueue
+
+object ThreadUtil {
+    fun runOnClientThread(block: () -> Unit) {
+        client.add(block)
+    }
+
+    fun runOnServerThread(block: () -> Unit) {
+        server.add(block)
+    }
+
+    @SubscribeEvent
+    fun onClientTick(e: TickEvent.ClientTickEvent) {
+        while (true) (client.poll() ?: return)()
+    }
+
+    @SubscribeEvent
+    fun onServerTick(e: TickEvent.ServerTickEvent) {
+        while (true) (server.poll() ?: return)()
+    }
+
+    private val client = ConcurrentLinkedQueue<() -> Unit>()
+    private val server = ConcurrentLinkedQueue<() -> Unit>()
+}
diff --git a/src/main/java/com/anatawa12/fixRtm/network/NotifyUntracked.kt b/src/main/java/com/anatawa12/fixRtm/network/NotifyUntracked.kt
index 21967f9e..fe018700 100644
--- a/src/main/java/com/anatawa12/fixRtm/network/NotifyUntracked.kt
+++ b/src/main/java/com/anatawa12/fixRtm/network/NotifyUntracked.kt
@@ -1,6 +1,7 @@
 package com.anatawa12.fixRtm.network
 
 import com.anatawa12.fixRtm.Loggers
+import com.anatawa12.fixRtm.ThreadUtil
 import io.netty.buffer.ByteBuf
 import net.minecraft.world.WorldServer
 import net.minecraftforge.fml.common.network.simpleimpl.IMessage
@@ -30,14 +31,16 @@ class NotifyUntracked : IMessage {
 
     companion object : IMessageHandler<NotifyUntracked, Nothing?> {
         override fun onMessage(message: NotifyUntracked, ctx: MessageContext): Nothing? {
-            val entry = ctx.serverHandler.player.world
-                .let { it as WorldServer }
-                .entityTracker
-                .trackedEntityHashTable
-                .lookup(message.entityId)
-                ?: return null.also { logger.error("entry for #${message.entityId} not found") }
-
-            entry.trackingPlayers.remove(ctx.serverHandler.player)
+            val world = ctx.serverHandler.player.world as WorldServer
+            ThreadUtil.runOnServerThread {
+                val entry = world
+                    .entityTracker
+                    .trackedEntityHashTable
+                    .lookup(message.entityId)
+                    ?: return@runOnServerThread logger.error("entry for #${message.entityId} not found")
+
+                entry.trackingPlayers.remove(ctx.serverHandler.player)
+            }
 
             return null
         }