diff --git a/mqtt5properties.cpp b/mqtt5properties.cpp
index ab01aca..2a543de 100644
--- a/mqtt5properties.cpp
+++ b/mqtt5properties.cpp
@@ -152,7 +152,7 @@ void Mqtt5PropertyBuilder::writeStr(Mqtt5Properties prop, const std::string &str
     const uint16_t strlen = str.length();
 
     size_t pos = genericBytes.size();
-    const size_t newSize = pos + strlen + 2;
+    const size_t newSize = pos + strlen + 3;
     genericBytes.resize(newSize);
 
     const uint8_t a = static_cast<uint8_t>(strlen >> 8);
diff --git a/mqttpacket.cpp b/mqttpacket.cpp
index 9a58834..18d2f03 100644
--- a/mqttpacket.cpp
+++ b/mqttpacket.cpp
@@ -33,6 +33,7 @@ MqttPacket::MqttPacket(CirBuf &buf, size_t packet_len, size_t fixed_header_lengt
     assert(packet_len > 0);
     buf.read(bites.data(), packet_len);
 
+    protocolVersion = sender->getProtocolVersion();
     first_byte = bites[0];
     unsigned char _packetType = (first_byte & 0xF0) >> 4;
     packetType = (PacketType)_packetType;
@@ -758,10 +759,12 @@ void MqttPacket::handlePublish()
         const size_t proplen = decodeVariableByteIntAtPos();
         const size_t prop_end_at = pos + proplen;
 
+        if (proplen > 0)
+            publishData.propertyBuilder = std::make_shared<Mqtt5PropertyBuilder>();
+
         while (pos < prop_end_at)
         {
             const Mqtt5Properties prop = static_cast<Mqtt5Properties>(readByte());
-            publishData.propertyBuilder = std::make_shared<Mqtt5PropertyBuilder>();
 
             switch (prop)
             {
@@ -1131,6 +1134,21 @@ const Publish &MqttPacket::getPublishData()
     return publishData;
 }
 
+bool MqttPacket::containsClientSpecificProperties() const
+{
+    assert(packetType == PacketType::PUBLISH);
+
+    if (protocolVersion <= ProtocolVersion::Mqtt311 || !publishData.propertyBuilder)
+        return false;
+
+    if (publishData.createdAt.time_since_epoch().count() == 0) // TODO: better
+    {
+        return true;
+    }
+
+    return false;
+}
+
 void MqttPacket::readIntoBuf(CirBuf &buf) const
 {
     assert(packetType != PacketType::PUBLISH || (first_byte & 0b00000110) >> 1 == publishData.qos);
diff --git a/mqttpacket.h b/mqttpacket.h
index ade9f89..b98b8dd 100644
--- a/mqttpacket.h
+++ b/mqttpacket.h
@@ -122,6 +122,7 @@ public:
     bool getRetain() const;
     void setRetain();
     const Publish &getPublishData();
+    bool containsClientSpecificProperties() const;
 };
 
 #endif // MQTTPACKET_H
diff --git a/publishcopyfactory.cpp b/publishcopyfactory.cpp
index 47e85f9..bf3a60a 100644
--- a/publishcopyfactory.cpp
+++ b/publishcopyfactory.cpp
@@ -21,7 +21,16 @@ MqttPacket *PublishCopyFactory::getOptimumPacket(const char max_qos, const Proto
 {
     if (packet)
     {
-        // TODO: you can't do this when there are client specific mqtt5 properties
+        if (packet->containsClientSpecificProperties())
+        {
+            Publish newPublish(packet->getPublishData());
+            newPublish.splitTopic = false;
+            newPublish.qos = max_qos;
+            newPublish.setClientSpecificProperties();
+            this->oneShotPacket = std::make_unique<MqttPacket>(protocolVersion, newPublish);
+            return this->oneShotPacket.get();
+        }
+
         if (packet->getProtocolVersion() == protocolVersion && orgQos == max_qos)
         {
             assert(orgQos == packet->getQos());
diff --git a/types.cpp b/types.cpp
index 02a5ee4..3ee73bc 100644
--- a/types.cpp
+++ b/types.cpp
@@ -126,7 +126,18 @@ void PublishBase::setClientSpecificProperties()
 {
     if (propertyBuilder)
         propertyBuilder->clearClientSpecificBytes();
-    // TODO. Expires at?
+
+    auto now = std::chrono::steady_clock::now();
+    std::chrono::seconds newExpiresAfter = std::chrono::duration_cast<std::chrono::seconds>(now - createdAt);
+
+    if (newExpiresAfter.count() > 0)
+        propertyBuilder->writeMessageExpiryInterval(newExpiresAfter.count());
+}
+
+bool PublishBase::hasExpired() const
+{
+    auto now = std::chrono::steady_clock::now();
+    return (createdAt + expiresAfter) > now;
 }
 
 Publish::Publish(const Publish &other) :
diff --git a/types.h b/types.h
index a155290..595472e 100644
--- a/types.h
+++ b/types.h
@@ -67,7 +67,7 @@ enum class Mqtt5Properties
     SubscriptionIdentifier = 11,
     SessionExpiryInterval = 17,
     AssignedClientIdentifier = 18,
-    ServerKeepAlive = 13,
+    ServerKeepAlive = 19,
     AuthenticationMethod = 21,
     AuthenticationData = 22,
     RequestProblemInformation = 23,
@@ -203,12 +203,13 @@ public:
     bool splitTopic = true;
     std::chrono::time_point<std::chrono::steady_clock> createdAt;
     std::chrono::seconds expiresAfter;
-    std::shared_ptr<Mqtt5PropertyBuilder> propertyBuilder;
+    std::shared_ptr<Mqtt5PropertyBuilder> propertyBuilder; // Only contains data for sending, not receiving
 
     PublishBase() = default;
     PublishBase(const std::string &topic, const std::string &payload, char qos);
     size_t getLengthWithoutFixedHeader() const;
     void setClientSpecificProperties();
+    bool hasExpired() const;
 };
 
 class Publish : public PublishBase