diff --git a/CMakeLists.txt b/CMakeLists.txt
index b9c47d4a18..21c3d4dfc8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -49,6 +49,7 @@ endif ()
 
 # Find packages.
 find_package(OpenSSL 3.0.0 REQUIRED COMPONENTS Crypto)
+find_package(ZLIB REQUIRED)
 
 find_package(fmt 8.1.1 CONFIG)
 if (NOT fmt_FOUND)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3c09a5a534..d89e2beecb 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -178,6 +178,7 @@ target_link_libraries(tfslib PRIVATE
 	fmt::fmt
 	OpenSSL::Crypto
 	pugixml::pugixml
+	ZLIB::ZLIB
 	${CMAKE_THREAD_LIBS_INIT}
 	${LUA_LIBRARIES}
 	${MYSQL_CLIENT_LIBS}
diff --git a/src/outputmessage.h b/src/outputmessage.h
index 402a4dc6f0..2741572ca5 100644
--- a/src/outputmessage.h
+++ b/src/outputmessage.h
@@ -21,12 +21,12 @@ class OutputMessage : public NetworkMessage
 
 	void writeMessageLength() { add_header(info.length); }
 
-	void addCryptoHeader(checksumMode_t mode, uint32_t& sequence)
+	void addCryptoHeader(checksumMode_t mode)
 	{
 		if (mode == CHECKSUM_ADLER) {
 			add_header(adlerChecksum(&buffer[outputBufferStart], info.length));
 		} else if (mode == CHECKSUM_SEQUENCE) {
-			add_header(sequence++);
+			add_header(getSequenceId());
 		}
 
 		writeMessageLength();
@@ -48,6 +48,9 @@ class OutputMessage : public NetworkMessage
 		info.position += msgLen;
 	}
 
+	void setSequenceId(uint32_t sequence) { sequenceId = sequence; }
+	uint32_t getSequenceId() const { return sequenceId; }
+
 private:
 	template <typename T>
 	void add_header(T add)
@@ -60,6 +63,7 @@ class OutputMessage : public NetworkMessage
 	}
 
 	MsgSize_t outputBufferStart = INITIAL_BUFFER_POSITION;
+	uint32_t sequenceId;
 };
 
 namespace tfs::net {
diff --git a/src/protocol.cpp b/src/protocol.cpp
index 71b7f6c554..2077a89134 100644
--- a/src/protocol.cpp
+++ b/src/protocol.cpp
@@ -46,11 +46,20 @@ bool XTEA_decrypt(NetworkMessage& msg, const xtea::round_keys& key)
 void Protocol::onSendMessage(const OutputMessage_ptr& msg)
 {
 	if (!rawMessages) {
+		if (encryptionEnabled && checksumMode == CHECKSUM_SEQUENCE) {
+			uint32_t compressionChecksum = 0;
+			if (msg->getLength() >= 128 && deflateMessage(*msg)) {
+				compressionChecksum = 0x80000000;
+			}
+
+			msg->setSequenceId(compressionChecksum | getNextSequenceId());
+		}
+
 		msg->writeMessageLength();
 
 		if (encryptionEnabled) {
 			XTEA_encrypt(*msg, key);
-			msg->addCryptoHeader(checksumMode, sequenceNumber);
+			msg->addCryptoHeader(checksumMode);
 		}
 	}
 }
@@ -86,6 +95,37 @@ bool Protocol::RSA_decrypt(NetworkMessage& msg)
 	return msg.getByte() == 0;
 }
 
+bool Protocol::deflateMessage(OutputMessage& msg)
+{
+	static thread_local std::vector<uint8_t> buffer(NETWORKMESSAGE_MAXSIZE);
+
+	zstream.next_in = msg.getOutputBuffer();
+	zstream.avail_in = msg.getLength();
+	zstream.next_out = buffer.data();
+	zstream.avail_out = buffer.size();
+
+	const auto result = deflate(&zstream, Z_FINISH);
+	if (result != Z_OK && result != Z_STREAM_END) {
+		std::cout << "Error while deflating packet data error: " << (zstream.msg ? zstream.msg : "unknown")
+		          << std::endl;
+		return false;
+	}
+
+	const auto size = zstream.total_out;
+	deflateReset(&zstream);
+
+	if (size <= 0) {
+		std::cout << "Deflated packet data had invalid size: " << size
+		          << " error: " << (zstream.msg ? zstream.msg : "unknown") << std::endl;
+		return false;
+	}
+
+	msg.reset();
+	msg.addBytes(reinterpret_cast<const char*>(buffer.data()), size);
+
+	return true;
+}
+
 Connection::Address Protocol::getIP() const
 {
 	if (auto connection = getConnection()) {
diff --git a/src/protocol.h b/src/protocol.h
index a6ea13dddf..639993b1ed 100644
--- a/src/protocol.h
+++ b/src/protocol.h
@@ -7,10 +7,17 @@
 #include "connection.h"
 #include "xtea.h"
 
+#include <zlib.h>
+
 class Protocol : public std::enable_shared_from_this<Protocol>
 {
 public:
-	explicit Protocol(Connection_ptr connection) : connection(connection) {}
+	explicit Protocol(Connection_ptr connection) : connection(connection)
+	{
+		if (deflateInit2(&zstream, 6, Z_DEFLATED, -15, 8, Z_DEFAULT_STRATEGY) != Z_OK) {
+			std::cout << "ZLIB initialization error: " << (zstream.msg ? zstream.msg : "unknown") << std::endl;
+		}
+	}
 	virtual ~Protocol() = default;
 
 	// non-copyable
@@ -42,6 +49,16 @@ class Protocol : public std::enable_shared_from_this<Protocol>
 		}
 	}
 
+	uint32_t getNextSequenceId()
+	{
+		const auto sequence = ++sequenceNumber;
+		if (sequenceNumber >= static_cast<uint32_t>(std::numeric_limits<int32_t>::max())) {
+			sequenceNumber = 0;
+		}
+
+		return sequence;
+	}
+
 protected:
 	static constexpr size_t RSA_BUFFER_LENGTH = 128;
 
@@ -57,6 +74,8 @@ class Protocol : public std::enable_shared_from_this<Protocol>
 
 	static bool RSA_decrypt(NetworkMessage& msg);
 
+	bool deflateMessage(OutputMessage& msg);
+
 	void setRawMessages(bool value) { rawMessages = value; }
 
 	virtual void release() {}
@@ -72,6 +91,8 @@ class Protocol : public std::enable_shared_from_this<Protocol>
 	bool encryptionEnabled = false;
 	checksumMode_t checksumMode = CHECKSUM_ADLER;
 	bool rawMessages = false;
+
+	z_stream zstream{};
 };
 
 #endif // FS_PROTOCOL_H
diff --git a/src/protocolgame.cpp b/src/protocolgame.cpp
index f1cb31f884..ee5d981e7f 100644
--- a/src/protocolgame.cpp
+++ b/src/protocolgame.cpp
@@ -383,7 +383,7 @@ void ProtocolGame::onRecvFirstMessage(NetworkMessage& msg)
 	}
 
 	// Change packet verifying mode for QT clients
-	if (version >= 1111 && operatingSystem >= CLIENTOS_QT_LINUX && operatingSystem < CLIENTOS_OTCLIENT_LINUX) {
+	if (version >= 1111 && operatingSystem >= CLIENTOS_QT_LINUX && operatingSystem <= CLIENTOS_OTCLIENT_MAC) {
 		setChecksumMode(CHECKSUM_SEQUENCE);
 	}
 
diff --git a/vcpkg.json b/vcpkg.json
index eb7f23d7e2..d47df2137f 100644
--- a/vcpkg.json
+++ b/vcpkg.json
@@ -14,38 +14,27 @@
     },
     "libmariadb",
     "openssl",
-    "pugixml"
+    "pugixml",
+    "zlib"
   ],
   "features": {
     "http": {
       "description": "Enable HTTP support",
-      "dependencies": [
-        "boost-beast",
-        "boost-json"
-      ]
+      "dependencies": ["boost-beast", "boost-json"]
     },
     "lua": {
       "description": "Use Lua instead of LuaJIT",
-      "dependencies": [
-        "lua"
-      ]
+      "dependencies": ["lua"]
     },
     "luajit": {
       "description": "Use LuaJIT instead of Lua",
-      "dependencies": [
-        "luajit"
-      ]
+      "dependencies": ["luajit"]
     },
     "unit-tests": {
       "description": "Build unit tests",
-      "dependencies": [
-        "boost-test"
-      ]
+      "dependencies": ["boost-test"]
     }
   },
-  "default-features": [
-    "lua",
-    "http"
-  ],
+  "default-features": ["lua", "http"],
   "builtin-baseline": "215a2535590f1f63788ac9bd2ed58ad15e6afdff"
 }