diff --git a/irc.go b/irc.go
index 4e13886..10c0391 100644
--- a/irc.go
+++ b/irc.go
@@ -3,9 +3,9 @@
 // license that can be found in the LICENSE file.
 
 /*
-This package provides an event based IRC client library. It allows to 
-register callbacks for the events you need to handle. Its features 
-include handling standard CTCP, reconnecting on errors and detecting 
+This package provides an event based IRC client library. It allows to
+register callbacks for the events you need to handle. Its features
+include handling standard CTCP, reconnecting on errors and detecting
 stones servers.
 Details of the IRC protocol can be found in the following RFCs:
 https://tools.ietf.org/html/rfc1459
@@ -26,6 +26,7 @@ import (
 	"log"
 	"net"
 	"os"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -34,7 +35,6 @@ const (
 	VERSION = "go-ircevent v2.1"
 )
 
-
 // Read data from a connection. To be used as a goroutine.
 func (irc *Connection) readLoop() {
 	br := bufio.NewReaderSize(irc.socket, 512)
@@ -101,7 +101,6 @@ func (irc *Connection) readLoop() {
 	irc.readerExit <- true
 }
 
-
 // Loop to write to a connection. To be used as a goroutine.
 func (irc *Connection) writeLoop() {
 	for {
@@ -139,7 +138,6 @@ func (irc *Connection) writeLoop() {
 	irc.writerExit <- true
 }
 
-
 // Pings the server if we have not received any messages for 5 minutes
 // to keep the connection alive. To be used as a goroutine.
 func (irc *Connection) pingLoop() {
@@ -169,7 +167,6 @@ func (irc *Connection) pingLoop() {
 	}
 }
 
-
 // Main loop to control the connection.
 func (irc *Connection) Loop() {
 	for !irc.stopped {
@@ -190,7 +187,6 @@ func (irc *Connection) Loop() {
 	}
 }
 
-
 // Quit the current connection and disconnect from the server
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.1.6
 func (irc *Connection) Quit() {
@@ -199,60 +195,51 @@ func (irc *Connection) Quit() {
 	irc.Disconnect()
 }
 
-
 // Use the connection to join a given channel.
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.2.1
 func (irc *Connection) Join(channel string) {
 	irc.pwrite <- fmt.Sprintf("JOIN %s\r\n", channel)
 }
 
-
 // Leave a given channel.
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.2.2
 func (irc *Connection) Part(channel string) {
 	irc.pwrite <- fmt.Sprintf("PART %s\r\n", channel)
 }
 
-
 // Send a notification to a nickname. This is similar to Privmsg but must not receive replies.
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.4.2
 func (irc *Connection) Notice(target, message string) {
 	irc.pwrite <- fmt.Sprintf("NOTICE %s :%s\r\n", target, message)
 }
 
-
 // Send a formated notification to a nickname.
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.4.2
 func (irc *Connection) Noticef(target, format string, a ...interface{}) {
 	irc.Notice(target, fmt.Sprintf(format, a...))
 }
 
-
 // Send (private) message to a target (channel or nickname).
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.4.1
 func (irc *Connection) Privmsg(target, message string) {
 	irc.pwrite <- fmt.Sprintf("PRIVMSG %s :%s\r\n", target, message)
 }
 
-
 // Send formated string to specified target (channel or nickname).
 func (irc *Connection) Privmsgf(target, format string, a ...interface{}) {
 	irc.Privmsg(target, fmt.Sprintf(format, a...))
 }
 
-
 // Send raw string.
 func (irc *Connection) SendRaw(message string) {
 	irc.pwrite <- message + "\r\n"
 }
 
-
 // Send raw formated string.
 func (irc *Connection) SendRawf(format string, a ...interface{}) {
 	irc.SendRaw(fmt.Sprintf(format, a...))
 }
 
-
 // Set (new) nickname.
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.1.2
 func (irc *Connection) Nick(n string) {
@@ -260,27 +247,23 @@ func (irc *Connection) Nick(n string) {
 	irc.SendRawf("NICK %s", n)
 }
 
-
 // Determine nick currently used with the connection.
 func (irc *Connection) GetNick() string {
 	return irc.nickcurrent
 }
 
-
 // Query information about a particular nickname.
 // RFC 1459: https://tools.ietf.org/html/rfc1459#section-4.5.2
 func (irc *Connection) Whois(nick string) {
 	irc.SendRawf("WHOIS %s", nick)
 }
 
-
 // Query information about a given nickname in the server.
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.5.1
 func (irc *Connection) Who(nick string) {
 	irc.SendRawf("WHO %s", nick)
 }
 
-
 // Set different modes for a target (channel or nickname).
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.2.3
 func (irc *Connection) Mode(target string, modestring ...string) {
@@ -292,8 +275,7 @@ func (irc *Connection) Mode(target string, modestring ...string) {
 	irc.SendRawf("MODE %s", target)
 }
 
-
-// A disconnect sends all buffered messages (if possible), 
+// A disconnect sends all buffered messages (if possible),
 // stops all goroutines and then closes the socket.
 func (irc *Connection) Disconnect() {
 	irc.endping <- true
@@ -314,13 +296,11 @@ func (irc *Connection) Disconnect() {
 	irc.Error <- errors.New("Disconnect Called")
 }
 
-
 // Reconnect to a server using the current connection.
 func (irc *Connection) Reconnect() error {
 	return irc.Connect(irc.server)
 }
 
-
 // Connect to a given server using the current connection configuration.
 // This function also takes care of identification if a password is provided.
 // RFC 1459 details: https://tools.ietf.org/html/rfc1459#section-4.1
@@ -328,7 +308,38 @@ func (irc *Connection) Connect(server string) error {
 	irc.server = server
 	irc.stopped = false
 
-	var err error
+	// make sure everything is ready for connection
+	if len(irc.server) == 0 {
+		return errors.New("empty 'server'")
+	}
+	if strings.Count(irc.server, ":") != 1 {
+		return errors.New("wrong number of ':' in address")
+	}
+	if strings.Index(irc.server, ":") == 0 {
+		return errors.New("hostname is missing")
+	}
+	if strings.Index(irc.server, ":") == len(irc.server)-1 {
+		return errors.New("port missing")
+	}
+	// check for valid range
+	ports := strings.Split(irc.server, ":")[1]
+	port, err := strconv.Atoi(ports)
+	if err != nil {
+		return errors.New("extracting port failed")
+	}
+	if !((port >= 0) && (port <= 65535)) {
+		return errors.New("port number outside valid range")
+	}
+	if irc.Log == nil {
+		return errors.New("'Log' points to nil")
+	}
+	if len(irc.nick) == 0 {
+		return errors.New("empty 'user'")
+	}
+	if len(irc.user) == 0 {
+		return errors.New("empty 'user'")
+	}
+
 	if irc.UseTLS {
 		if irc.netsock, err = net.DialTimeout("tcp", irc.server, irc.Timeout); err == nil {
 			irc.socket = tls.Client(irc.netsock, irc.TLSConfig)
@@ -357,10 +368,18 @@ func (irc *Connection) Connect(server string) error {
 	return nil
 }
 
-
 // Create a connection with the (publicly visible) nickname and username.
-// The nickname is later used to address the user.
+// The nickname is later used to address the user. Returns nil if nick
+// or user are empty.
 func IRC(nick, user string) *Connection {
+	// catch invalid values
+	if len(nick) == 0 {
+		return nil
+	}
+	if len(user) == 0 {
+		return nil
+	}
+
 	irc := &Connection{
 		nick:       nick,
 		user:       user,
diff --git a/irc_test.go b/irc_test.go
index 02fe5b4..36c4374 100644
--- a/irc_test.go
+++ b/irc_test.go
@@ -12,6 +12,7 @@ func TestConnection(t *testing.T) {
 	irccon.Debug = true
 	err := irccon.Connect("irc.freenode.net:6667")
 	if err != nil {
+		t.Log(err.Error())
 		t.Fatal("Can't connect to freenode.")
 	}
 	irccon.AddCallback("001", func(e *Event) { irccon.Join("#go-eventirc") })
@@ -36,6 +37,7 @@ func TestConnectionSSL(t *testing.T) {
 	irccon.UseTLS = true
 	err := irccon.Connect("irc.freenode.net:7000")
 	if err != nil {
+		t.Log(err.Error())
 		t.Fatal("Can't connect to freenode.")
 	}
 	irccon.AddCallback("001", func(e *Event) { irccon.Join("#go-eventirc") })
@@ -49,6 +51,83 @@ func TestConnectionSSL(t *testing.T) {
 	irccon.Loop()
 }
 
+func TestConnectionEmtpyServer(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	err := irccon.Connect("")
+	if err == nil {
+		t.Fatal("emtpy server string not detected")
+	}
+}
+
+func TestConnectionDoubleColon(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	err := irccon.Connect("::")
+	if err == nil {
+		t.Fatal("wrong number of ':' not detected")
+	}
+}
+
+func TestConnectionMissingHost(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	err := irccon.Connect(":6667")
+	if err == nil {
+		t.Fatal("missing host not detected")
+	}
+}
+
+func TestConnectionMissingPort(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	err := irccon.Connect("chat.freenode.net:")
+	if err == nil {
+		t.Fatal("missing port not detected")
+	}
+}
+
+func TestConnectionNegativePort(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	err := irccon.Connect("chat.freenode.net:-1")
+	if err == nil {
+		t.Fatal("negative port number not detected")
+	}
+}
+
+func TestConnectionTooLargePort(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	err := irccon.Connect("chat.freenode.net:65536")
+	if err == nil {
+		t.Fatal("too large port number not detected")
+	}
+}
+
+func TestConnectionMissingLog(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	irccon.Log = nil
+	err := irccon.Connect("chat.freenode.net:6667")
+	if err == nil {
+		t.Fatal("missing 'Log' not detected")
+	}
+}
+
+func TestConnectionEmptyUser(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	// user may be changed after creation
+	irccon.user = ""
+	err := irccon.Connect("chat.freenode.net:6667")
+	if err == nil {
+		t.Fatal("empty 'user' not detected")
+	}
+}
+
+func TestConnectionEmptyNick(t *testing.T) {
+	irccon := IRC("go-eventirc", "go-eventirc")
+	// nick may be changed after creation
+	irccon.nick = ""
+	err := irccon.Connect("chat.freenode.net:6667")
+	if err == nil {
+		t.Fatal("empty 'nick' not detected")
+	}
+}
+
 func TestRemoveCallback(t *testing.T) {
 	irccon := IRC("go-eventirc", "go-eventirc")
 	irccon.VerboseCallbackHandler = true
@@ -127,3 +206,19 @@ func TestClearCallback(t *testing.T) {
 		t.Error("Callbacks not cleared")
 	}
 }
+
+func TestIRCemptyNick(t *testing.T) {
+	irccon := IRC("", "go-eventirc")
+	irccon = nil
+	if irccon != nil {
+		t.Error("empty nick didn't result in error")
+		t.Fail()
+	}
+}
+ 
+func TestIRCemptyUser(t *testing.T) {
+	irccon := IRC("go-eventirc", "")
+	if irccon != nil {
+		t.Error("empty user didn't result in error")
+	}
+}