diff --git a/Reactor/Networking/Messages/ModdedHandshakeC2S.cs b/Reactor/Networking/Messages/ModdedHandshakeC2S.cs
index a90f4e4..7ef4aeb 100644
--- a/Reactor/Networking/Messages/ModdedHandshakeC2S.cs
+++ b/Reactor/Networking/Messages/ModdedHandshakeC2S.cs
@@ -1,10 +1,31 @@
 using System.Collections.Generic;
+using System.Text;
 using Hazel;
 
 namespace Reactor.Networking.Messages;
 
 internal static class ModdedHandshakeC2S
 {
+    private const int MaxPackedSize = 5;
+
+    public static int GetMaxSerializedSize(IReadOnlyCollection<Mod> mods)
+    {
+        var size = MaxPackedSize;
+
+        foreach (var mod in mods)
+        {
+            size += GetMaxStringSize(mod.Id) + GetMaxStringSize(mod.Version) + sizeof(ushort);
+            if (mod.IsRequiredOnAllClients) size += GetMaxStringSize(mod.Name);
+        }
+
+        return size;
+    }
+
+    private static int GetMaxStringSize(string? value)
+    {
+        return MaxPackedSize + (value == null ? 0 : Encoding.UTF8.GetByteCount(value));
+    }
+
     public static void Serialize(MessageWriter writer, IReadOnlyCollection<Mod> mods)
     {
         writer.WritePacked(mods.Count);
diff --git a/Reactor/Networking/Patches/ClientPatches.cs b/Reactor/Networking/Patches/ClientPatches.cs
index a9c9f6b..e5bfcfe 100644
--- a/Reactor/Networking/Patches/ClientPatches.cs
+++ b/Reactor/Networking/Patches/ClientPatches.cs
@@ -358,16 +358,14 @@ public static void Prefix(ref bool useDtlsLayout)
 
         public static void Postfix(ref Il2CppStructArray<byte> __result)
         {
-            var handshake = new MessageWriter(1000);
+            var mods = ModList.Current;
+            var handshake = new MessageWriter(__result.Length + ReactorHeader.Size + ModdedHandshakeC2S.GetMaxSerializedSize(mods));
 
             handshake.Write(__result);
 
             ReactorHeader.Write(handshake);
 
-            ModdedHandshakeC2S.Serialize(
-                handshake,
-                ModList.Current
-            );
+            ModdedHandshakeC2S.Serialize(handshake, mods);
 
             __result = handshake.ToByteArray(true);
             handshake.Recycle();