diff --git a/bukkit/src/main/java/net/momirealms/craftengine/bukkit/plugin/network/PacketConsumers.java b/bukkit/src/main/java/net/momirealms/craftengine/bukkit/plugin/network/PacketConsumers.java
index 31acebdf2..eeabcac93 100644
--- a/bukkit/src/main/java/net/momirealms/craftengine/bukkit/plugin/network/PacketConsumers.java
+++ b/bukkit/src/main/java/net/momirealms/craftengine/bukkit/plugin/network/PacketConsumers.java
@@ -2290,7 +2290,7 @@ public class PacketConsumers {
     private static BukkitNetworkManager.Handlers simpleAddEntityHandler(EntityPacketHandler handler) {
         return (user, event) -> {
             FriendlyByteBuf buf = event.getBuffer();
-            user.entityPacketHandlers().put(buf.readVarInt(), handler);
+            user.entityPacketHandlers().putIfAbsent(buf.readVarInt(), handler);
         };
     }
 }
diff --git a/server-mod/v1_21_5/src/main/resources/mixins.craftengine.json b/server-mod/v1_21_5/src/main/resources/mixins.craftengine.json
index 288b6501f..69e19f9d0 100644
--- a/server-mod/v1_21_5/src/main/resources/mixins.craftengine.json
+++ b/server-mod/v1_21_5/src/main/resources/mixins.craftengine.json
@@ -6,7 +6,6 @@
   "target": "@env(DEFAULT)",
   "compatibilityLevel": "JAVA_21",
   "server": [
-    "BlocksMixin",
-    "ItemStackMixin"
+    "BlocksMixin"
   ]
 }