diff --git a/errorcodes/error_codes.go b/errorcodes/error_codes.go
new file mode 100644
index 00000000..7f063f8a
--- /dev/null
+++ b/errorcodes/error_codes.go
@@ -0,0 +1,32 @@
+package errorcodes
+
+import "github.com/lucas-clemente/quic-go/protocol"
+
+const (
+	QUIC_NO_ERROR                      = protocol.ErrorCode(0)
+	QUIC_STREAM_DATA_AFTER_TERMINATION = protocol.ErrorCode(2)
+	// QUIC_SERVER_ERROR_PROCESSING_STREAM= There was some server error which halted stream processing.
+	// QUIC_MULTIPLE_TERMINATION_OFFSETS= The sender received two mismatching fin or reset offsets for a single stream.
+	// QUIC_BAD_APPLICATION_PAYLOAD= The sender received bad application data.
+	QUIC_INVALID_PACKET_HEADER         = protocol.ErrorCode(3)
+	QUIC_INVALID_FRAME_DATA            = protocol.ErrorCode(4)
+	QUIC_INVALID_FEC_DATA              = protocol.ErrorCode(5)
+	QUIC_INVALID_RST_STREAM_DATA       = protocol.ErrorCode(6)
+	QUIC_INVALID_CONNECTION_CLOSE_DATA = protocol.ErrorCode(7)
+	QUIC_INVALID_ACK_DATA              = protocol.ErrorCode(9)
+	QUIC_DECRYPTION_FAILURE            = protocol.ErrorCode(12)
+	QUIC_ENCRYPTION_FAILURE            = protocol.ErrorCode(13)
+	QUIC_PACKET_TOO_LARGE              = protocol.ErrorCode(14)
+	// QUIC_PACKET_FOR_NONEXISTENT_STREAM= Data was sent for a stream which did not exist.
+	// QUIC_CLIENT_GOING_AWAY= The client is going away (browser close, etc.)
+	// QUIC_SERVER_GOING_AWAY= The server is going away (restart etc.)
+	QUIC_INVALID_STREAM_ID     = protocol.ErrorCode(17)
+	QUIC_TOO_MANY_OPEN_STREAMS = protocol.ErrorCode(18)
+	// QUIC_CONNECTION_TIMED_OUT= We hit our pre-negotiated (or default) timeout
+	QUIC_CRYPTO_TAGS_OUT_OF_ORDER                = protocol.ErrorCode(29)
+	QUIC_CRYPTO_TOO_MANY_ENTRIES                 = protocol.ErrorCode(30)
+	QUIC_CRYPTO_INVALID_VALUE_LENGTH             = protocol.ErrorCode(31)
+	QUIC_CRYPTO_MESSAGE_AFTER_HANDSHAKE_COMPLETE = protocol.ErrorCode(32)
+	QUIC_INVALID_CRYPTO_MESSAGE_TYPE             = protocol.ErrorCode(33)
+	// QUIC_SEQUENCE_NUMBER_LIMIT_REACHED= Transmitting an additional packet would cause a packet number to be reused.
+)
diff --git a/server.go b/server.go
index 181da035..3eb816c9 100644
--- a/server.go
+++ b/server.go
@@ -59,9 +59,11 @@ func (s *Server) ListenAndServe(address string) error {
 		}
 		data = data[:n]
 		r := bytes.NewReader(data)
+		// ToDo: check packet size and send errorcodes.QUIC_PACKET_TOO_LARGE if packet is too large
 
 		publicHeader, err := ParsePublicHeader(r)
 		if err != nil {
+			// ToDo: send errorcodes.QUIC_INVALID_PACKET_HEADER
 			fmt.Printf("Could not parse public header")
 			continue
 		}
diff --git a/session.go b/session.go
index 9df216ad..b1e7c6cc 100644
--- a/session.go
+++ b/session.go
@@ -8,6 +8,7 @@ import (
 	"net"
 	"sync"
 
+	"github.com/lucas-clemente/quic-go/errorcodes"
 	"github.com/lucas-clemente/quic-go/frames"
 	"github.com/lucas-clemente/quic-go/handshake"
 	"github.com/lucas-clemente/quic-go/protocol"
@@ -140,6 +141,7 @@ func (s *Session) HandlePacket(addr *net.UDPAddr, publicHeaderBinary []byte, pub
 				err = fmt.Errorf("unknown frame type: %x", typeByte)
 			}
 			if err != nil {
+				s.Close(errorcodes.QUIC_INVALID_FRAME_DATA)
 				return err
 			}
 		}
@@ -228,6 +230,14 @@ func (s *Session) handleRstStreamFrame(r *bytes.Reader) error {
 	return nil
 }
 
+// Close closes the connection by sending a ConnectionClose frame
+func (s *Session) Close(errorCode protocol.ErrorCode) error {
+	frame := &frames.ConnectionCloseFrame{
+		ErrorCode: errorCode,
+	}
+	return s.SendFrame(frame)
+}
+
 // SendFrame sends a frame to the client
 func (s *Session) SendFrame(frame frames.Frame) error {
 	streamframe, ok := frame.(*frames.StreamFrame)