diff --git a/src/main/java/net/fabricmc/fabric/impl/network/PacketRegistryImpl.java b/src/main/java/net/fabricmc/fabric/impl/network/PacketRegistryImpl.java
index 96b7e4ef7..f20caf335 100644
--- a/src/main/java/net/fabricmc/fabric/impl/network/PacketRegistryImpl.java
+++ b/src/main/java/net/fabricmc/fabric/impl/network/PacketRegistryImpl.java
@@ -16,6 +16,7 @@
 
 package net.fabricmc.fabric.impl.network;
 
+import com.google.common.base.Charsets;
 import io.netty.buffer.Unpooled;
 import net.fabricmc.fabric.api.network.PacketConsumer;
 import net.fabricmc.fabric.api.network.PacketContext;
@@ -25,6 +26,7 @@ import net.minecraft.network.Packet;
 import net.minecraft.util.Identifier;
 import net.minecraft.util.PacketByteBuf;
 
+import java.nio.charset.StandardCharsets;
 import java.util.*;
 
 public abstract class PacketRegistryImpl implements PacketRegistry {
@@ -67,8 +69,14 @@ public abstract class PacketRegistryImpl implements PacketRegistry {
 
 	protected Packet<?> createRegisterTypePacket(Identifier id, Collection<Identifier> ids) {
 		PacketByteBuf buf = new PacketByteBuf(Unpooled.buffer());
+		boolean first = true;
 		for (Identifier a : ids) {
-			buf.writeString(a.toString());
+			if (!first) {
+				buf.writeByte(0);
+			} else {
+				first = false;
+			}
+			buf.writeBytes(a.toString().getBytes(StandardCharsets.US_ASCII));
 		}
 		return toPacket(id, buf);
 	}
@@ -84,9 +92,28 @@ public abstract class PacketRegistryImpl implements PacketRegistry {
 	public boolean accept(Identifier id, PacketContext context, PacketByteBuf buf) {
 		if (id.equals(PacketTypes.REGISTER) || id.equals(PacketTypes.UNREGISTER)) {
 			Collection<Identifier> ids = new HashSet<>();
-			while (buf.readerIndex() < buf.writerIndex() /* TODO: check correctness */) {
-				Identifier newId = new Identifier(buf.readString(32767));
-				ids.add(newId);
+
+			{
+				StringBuilder sb = new StringBuilder();
+				char c;
+
+				while (buf.readerIndex() < buf.writerIndex()) {
+					c = (char) buf.readByte();
+					if (c == 0) {
+						String s = sb.toString();
+						if (!s.isEmpty()) {
+							ids.add(new Identifier(s));
+						}
+						sb = new StringBuilder();
+					} else {
+						sb.append(c);
+					}
+				}
+
+				String s = sb.toString();
+				if (!s.isEmpty()) {
+					ids.add(new Identifier(s));
+				}
 			}
 
 			Collection<Identifier> target = getIdCollectionFor(context);
diff --git a/src/main/java/net/fabricmc/fabric/impl/network/PacketTypes.java b/src/main/java/net/fabricmc/fabric/impl/network/PacketTypes.java
index c9f3fa502..ec384aa92 100644
--- a/src/main/java/net/fabricmc/fabric/impl/network/PacketTypes.java
+++ b/src/main/java/net/fabricmc/fabric/impl/network/PacketTypes.java
@@ -19,9 +19,9 @@ package net.fabricmc.fabric.impl.network;
 import net.minecraft.util.Identifier;
 
 public final class PacketTypes {
-	static final Identifier BRAND = new Identifier("minecraft:brand");
-	static final Identifier REGISTER = new Identifier("minecraft:register");
-	static final Identifier UNREGISTER = new Identifier("minecraft:unregister");
+	public static final Identifier BRAND = new Identifier("minecraft:brand");
+	public static final Identifier REGISTER = new Identifier("minecraft:register");
+	public static final Identifier UNREGISTER = new Identifier("minecraft:unregister");
 
 	public static final Identifier OPEN_CONTAINER = new Identifier("fabric", "container/open");
 }
diff --git a/src/main/java/net/fabricmc/fabric/mixin/networking/MixinClientPlayNetworkHandler.java b/src/main/java/net/fabricmc/fabric/mixin/networking/MixinClientPlayNetworkHandler.java
index cff4985d5..f35a04d56 100644
--- a/src/main/java/net/fabricmc/fabric/mixin/networking/MixinClientPlayNetworkHandler.java
+++ b/src/main/java/net/fabricmc/fabric/mixin/networking/MixinClientPlayNetworkHandler.java
@@ -22,6 +22,7 @@ import net.fabricmc.fabric.api.network.ClientSidePacketRegistry;
 import net.fabricmc.fabric.api.network.PacketContext;
 import net.fabricmc.fabric.impl.network.ClientSidePacketRegistryImpl;
 import net.fabricmc.fabric.impl.network.PacketRegistryImpl;
+import net.fabricmc.fabric.impl.network.PacketTypes;
 import net.minecraft.class_2901;
 import net.minecraft.client.MinecraftClient;
 import net.minecraft.client.gui.Screen;
@@ -53,6 +54,14 @@ public abstract class MixinClientPlayNetworkHandler implements PacketContext {
 		sendPacket(PacketRegistryImpl.createInitialRegisterPacket(ClientSidePacketRegistry.INSTANCE));
 	}
 
+	// Optional hook: it only removes a warning message.
+	@Inject(method = "onCustomPayload", at = @At(value = "CONSTANT", args = "stringValue=Unknown custom packed identifier: {}"), cancellable = true, require = 0)
+	public void onCustomPayloadNotFound(CustomPayloadClientPacket packet, CallbackInfo info) {
+		if (packet.getChannel().equals(PacketTypes.REGISTER) || packet.getChannel().equals(PacketTypes.UNREGISTER)) {
+			info.cancel();
+		}
+	}
+
 	@Inject(method = "onCustomPayload", at = @At("HEAD"), cancellable = true)
 	public void onCustomPayload(CustomPayloadClientPacket packet, CallbackInfo info) {
 		if (((ClientSidePacketRegistryImpl) ClientSidePacketRegistry.INSTANCE).accept(packet.getChannel(), this, packet.getData())) {