diff --git a/connection.h b/connection.h
index b74b45d..a26eb98 100644
--- a/connection.h
+++ b/connection.h
@@ -117,12 +117,14 @@ private:
 	bool closeRequested;
 	unsigned long long closeTimeUs;
 	std::condition_variable_any closeAwaitCondition;
-	
+
+	friend class Protocol;
+	void open(Socket *socket);
+
 public:
 	Connection();
 	virtual ~Connection();
 	
-	void open(Socket *socket);
 	void close(ErrorCode errorCode = ERR_NONE);
 	
 	ReqId writeReq(const void *data, size_t size, void *userData = nullptr);
diff --git a/error.h b/error.h
index 38f55f3..3814c2b 100644
--- a/error.h
+++ b/error.h
@@ -19,6 +19,7 @@ enum : ErrorCode  {
 enum : ErrorCode  {
 	ERR_COMMON     = ERR_NONE + 1,
 	ERR_NOT_IMPLEMENTED,
+	ERR_INVALIDD_ARGS,
 };
 
 
diff --git a/handle.h b/handle.h
index c5402b7..1017b5f 100644
--- a/handle.h
+++ b/handle.h
@@ -209,8 +209,8 @@ public:
 		{ HandleBase::swap(other); return *this; }
 		
 	inline Type* pointer() const { return (Type*)HandleBase::get(); }
-	inline Type* operator->() const { return pointer(); }
-	inline Type& operator*() const { return *pointer(); }
+	inline Type* operator->() const { assert(pointer()); return pointer(); }
+	inline Type& operator*() const { assert(pointer()); return *pointer(); }
 	
 	template<typename TT>
 	inline operator Handle<TT>&()
diff --git a/protocol.cpp b/protocol.cpp
index f457467..57beaeb 100644
--- a/protocol.cpp
+++ b/protocol.cpp
@@ -75,6 +75,12 @@ Protocol::~Protocol()
 	{ assert(!first); }
 
 
+void Protocol::connectionOpen(const Connection::Handle &connection, Socket *socket) {
+	assert(connection && socket);
+	connection->open(socket);
+}
+
+
 void Protocol::closeAll() {
 	Lock lock(mutex);
 	while(first) 
diff --git a/protocol.h b/protocol.h
index 4e33d97..71fb875 100644
--- a/protocol.h
+++ b/protocol.h
@@ -105,6 +105,9 @@ protected:
 	inline Socket* socketSetUnchanged(Socket *socket)
 		{ socketCheck(socket, true); Socket *chNext = socket->chNext; socket->setChanged(false); return chNext; }
 
+	
+	// thread-safe methods
+	void connectionOpen(const Connection::Handle &connection, Socket *socket);
 	virtual void wakeup();
 
 public:
diff --git a/server.h b/server.h
index d9c5d27..5f45272 100644
--- a/server.h
+++ b/server.h
@@ -32,11 +32,13 @@ private:
 	Mutex mutex;
 	Socket *socket;
 	
+	friend class Protocol;
+	void open(Socket *socket);
+	
 public:
 	Server();
 	~Server();
 	
-	void open(Socket *socket);
 	void close(ErrorCode errorCode = ERR_NONE);
 	
 protected:
diff --git a/tcpprotocol.cpp b/tcpprotocol.cpp
index a18d182..44c2e6a 100644
--- a/tcpprotocol.cpp
+++ b/tcpprotocol.cpp
@@ -111,6 +111,7 @@ void TcpProtocol::threadRun() {
 
 ErrorCode TcpProtocol::connect(const Connection::Handle &connection, const Address &address) {
 	if (!thread) return ERR_PROTOCOL_NOT_INITIALIZED;
+	if (!connection) return ERR_INVALIDD_ARGS;
 
 	Address remoteAddres = address;
 	ErrorCode errorCode = resolve(remoteAddres);
@@ -125,7 +126,7 @@ ErrorCode TcpProtocol::connect(const Connection::Handle &connection, const Addre
 	}
 	
 	TcpSocket *socket = new TcpSocket(*this, connection, nullptr, remoteAddres, sockId);
-	connection->open(socket);
+	connectionOpen(connection, socket);
 	return ERR_NONE;
 }