diff --git a/datagram.go b/datagram.go
index 7277065..3417eba 100644
--- a/datagram.go
+++ b/datagram.go
@@ -30,7 +30,7 @@ func NewDatagramFrom(r io.Reader) (*Datagram, error) {
 		return nil, err
 	}
 
-	if !bytes.Equal([]byte{Reserved, Reserved}, buf[:1]) {
+	if !bytes.Equal([]byte{Reserved, Reserved}, buf[:2]) {
 		return nil, ErrBadDatagram
 	}