diff --git a/src/main/java/cpw/mods/fml/common/network/FMLIndexedMessageToMessageCodec.java b/src/main/java/cpw/mods/fml/common/network/FMLIndexedMessageToMessageCodec.java
index 6562d66813..a355a511a3 100644
--- a/src/main/java/cpw/mods/fml/common/network/FMLIndexedMessageToMessageCodec.java
+++ b/src/main/java/cpw/mods/fml/common/network/FMLIndexedMessageToMessageCodec.java
@@ -1,16 +1,14 @@
 package cpw.mods.fml.common.network;
 
-import java.util.List;
-
-import cpw.mods.fml.common.network.internal.FMLProxyPacket;
-
 import gnu.trove.map.hash.TByteObjectHashMap;
 import gnu.trove.map.hash.TObjectByteHashMap;
 import io.netty.buffer.ByteBuf;
 import io.netty.buffer.Unpooled;
-import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelHandler.Sharable;
+import io.netty.channel.ChannelHandlerContext;
 import io.netty.handler.codec.MessageToMessageCodec;
+import java.util.List;
+import cpw.mods.fml.common.network.internal.FMLProxyPacket;
 
 @Sharable
 public abstract class FMLIndexedMessageToMessageCodec<A> extends MessageToMessageCodec<FMLProxyPacket, A> {
@@ -43,6 +41,7 @@ public abstract class FMLIndexedMessageToMessageCodec<A> extends MessageToMessag
     @Override
     protected final void decode(ChannelHandlerContext ctx, FMLProxyPacket msg, List<Object> out) throws Exception
     {
+        testMessageValidity(msg);
         ByteBuf payload = msg.payload();
         byte discriminator = payload.readByte();
         Class<? extends A> clazz = discriminators.get(discriminator);
@@ -54,4 +53,13 @@ public abstract class FMLIndexedMessageToMessageCodec<A> extends MessageToMessag
         decodeInto(ctx, payload.slice(), newMsg);
         out.add(newMsg);
     }
+
+    /**
+     * Called to verify the message received. This can be used to hard disconnect in case of an unexpected packet,
+     * say due to a weird protocol mismatch. Use with caution.
+     * @param msg
+     */
+    protected void testMessageValidity(FMLProxyPacket msg)
+    {
+    }
 }
diff --git a/src/main/java/cpw/mods/fml/common/network/internal/FMLProxyPacket.java b/src/main/java/cpw/mods/fml/common/network/internal/FMLProxyPacket.java
index 3f8732125c..af1e97596a 100644
--- a/src/main/java/cpw/mods/fml/common/network/internal/FMLProxyPacket.java
+++ b/src/main/java/cpw/mods/fml/common/network/internal/FMLProxyPacket.java
@@ -10,6 +10,9 @@ import net.minecraft.network.Packet;
 import net.minecraft.network.PacketBuffer;
 import net.minecraft.network.play.client.C17PacketCustomPayload;
 import net.minecraft.network.play.server.S3FPacketCustomPayload;
+import org.apache.logging.log4j.Level;
+import cpw.mods.fml.common.FMLLog;
+import cpw.mods.fml.common.network.FMLNetworkException;
 import cpw.mods.fml.common.network.NetworkRegistry;
 import cpw.mods.fml.common.network.handshake.NetworkDispatcher;
 import cpw.mods.fml.relauncher.Side;
@@ -63,7 +66,20 @@ public class FMLProxyPacket extends Packet {
         if (internalChannel != null)
         {
             internalChannel.attr(NetworkRegistry.NET_HANDLER).set(this.netHandler);
-            internalChannel.writeInbound(this);
+            try
+            {
+                internalChannel.writeInbound(this);
+            }
+            catch (FMLNetworkException ne)
+            {
+                FMLLog.log(Level.ERROR, ne, "There was a network exception handling a packet on channel %s", channel);
+                dispatcher.rejectHandshake(ne.getMessage());
+            }
+            catch (Throwable t)
+            {
+                FMLLog.log(Level.ERROR, t, "There was a critical exception handling a packet on channel %s", channel);
+                dispatcher.rejectHandshake("A fatal error has occured, this connection is terminated");
+            }
         }
     }
 
diff --git a/src/main/java/cpw/mods/fml/common/network/internal/FMLRuntimeCodec.java b/src/main/java/cpw/mods/fml/common/network/internal/FMLRuntimeCodec.java
index 1d611a4eb5..d1f6ba99cc 100644
--- a/src/main/java/cpw/mods/fml/common/network/internal/FMLRuntimeCodec.java
+++ b/src/main/java/cpw/mods/fml/common/network/internal/FMLRuntimeCodec.java
@@ -1,8 +1,11 @@
 package cpw.mods.fml.common.network.internal;
 
-import cpw.mods.fml.common.network.FMLIndexedMessageToMessageCodec;
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
+import com.google.common.primitives.Bytes;
+import cpw.mods.fml.common.FMLLog;
+import cpw.mods.fml.common.network.FMLIndexedMessageToMessageCodec;
+import cpw.mods.fml.common.network.FMLNetworkException;
 
 public class FMLRuntimeCodec extends FMLIndexedMessageToMessageCodec<FMLMessage> {
     public FMLRuntimeCodec()
@@ -24,4 +27,16 @@ public class FMLRuntimeCodec extends FMLIndexedMessageToMessageCodec<FMLMessage>
         msg.fromBytes(source);
     }
 
+    @Override
+    protected void testMessageValidity(FMLProxyPacket msg)
+    {
+        if (msg.payload().getByte(0) == 0 && msg.payload().readableBytes() > 2)
+        {
+            FMLLog.severe("The connection appears to have sent an invalid FML packet of type 0, this is likely because it think's it's talking to 1.6.4 FML");
+            byte[] badData = new byte[msg.payload().readableBytes()];
+            msg.payload().getBytes(0, badData);
+            FMLLog.info("Bad data : %s",Bytes.asList(badData));
+            throw new FMLNetworkException("Invalid FML packet");
+        }
+    }
 }