diff --git a/MQTTnet.Core/Serializer/MqttPacketReader.cs b/MQTTnet.Core/Serializer/MqttPacketReader.cs
index f7fbdb2..417c19a 100644
--- a/MQTTnet.Core/Serializer/MqttPacketReader.cs
+++ b/MQTTnet.Core/Serializer/MqttPacketReader.cs
@@ -1,6 +1,8 @@
 using System;
 using System.IO;
 using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
 using MQTTnet.Core.Adapter;
 using MQTTnet.Core.Exceptions;
 using MQTTnet.Core.Protocol;
@@ -20,11 +22,11 @@ namespace MQTTnet.Core.Serializer
 
         public bool EndOfRemainingData => BaseStream.Position == _receivedMqttPacket.Header.BodyLength;
 
-        public static MqttPacketHeader ReadHeaderFromSource(Stream stream)
+        public static MqttPacketHeader ReadHeaderFromSource(Stream stream, CancellationToken cancellationToken)
         {
             var fixedHeader = (byte)stream.ReadByte();
             var controlPacketType = (MqttControlPacketType)(fixedHeader >> 4);
-            var bodyLength = ReadBodyLengthFromSource(stream);
+            var bodyLength = ReadBodyLengthFromSource(stream, cancellationToken);
 
             return new MqttPacketHeader
             {
@@ -62,7 +64,7 @@ namespace MQTTnet.Core.Serializer
             return ReadBytes(_receivedMqttPacket.Header.BodyLength - (int)BaseStream.Position);
         }
 
-        private static int ReadBodyLengthFromSource(Stream stream)
+        private static int ReadBodyLengthFromSource(Stream stream, CancellationToken cancellationToken)
         {
             // Alorithm taken from http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html.
             var multiplier = 1;
@@ -70,6 +72,11 @@ namespace MQTTnet.Core.Serializer
             byte encodedByte;
             do
             {
+                if (cancellationToken.IsCancellationRequested)
+                {
+                    throw new TaskCanceledException();
+                }
+
                 encodedByte = (byte)stream.ReadByte();
                 value += (encodedByte & 127) * multiplier;
                 multiplier *= 128;
diff --git a/MQTTnet.Core/Serializer/MqttPacketSerializer.cs b/MQTTnet.Core/Serializer/MqttPacketSerializer.cs
index fcec63c..f43fc72 100644
--- a/MQTTnet.Core/Serializer/MqttPacketSerializer.cs
+++ b/MQTTnet.Core/Serializer/MqttPacketSerializer.cs
@@ -546,6 +546,8 @@ namespace MQTTnet.Core.Serializer
 
         private static byte Serialize(MqttSubscribePacket packet, MqttPacketWriter writer)
         {
+            if (!packet.TopicFilters.Any()) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.8.3-3].");
+
             writer.Write(packet.PacketIdentifier);
 
             if (packet.TopicFilters?.Count > 0)
@@ -577,6 +579,8 @@ namespace MQTTnet.Core.Serializer
 
         private static byte Serialize(MqttUnsubscribePacket packet, MqttPacketWriter writer)
         {
+            if (!packet.TopicFilters.Any()) throw new MqttProtocolViolationException("At least one topic filter must be set [MQTT-3.10.3-2].");
+
             writer.Write(packet.PacketIdentifier);
 
             if (packet.TopicFilters?.Any() == true)