diff --git a/defaults.go b/defaults.go
index 7c5ecae0..63165b4f 100644
--- a/defaults.go
+++ b/defaults.go
@@ -150,11 +150,14 @@ func (dns *Msg) IsEdns0() *OPT {
 	return nil
 }
 
-// IsDomainName checks if s is a valid domainname, it returns
-// the number of labels and true, when a domain name is valid.
-// Note that non fully qualified domain name is considered valid, in this case the
-// last label is counted in the number of labels.
-// When false is returned the number of labels is not defined.
+// IsDomainName checks if s is a valid domain name, it returns the number of
+// labels and true, when a domain name is valid.  Note that non fully qualified
+// domain name is considered valid, in this case the last label is counted in
+// the number of labels.  When false is returned the number of labels is not
+// defined.  Also note that this function is extremely liberal; almost any
+// string is a valid domain name as the DNS is 8 bit protocol. It checks if each
+// label fits in 63 characters, but there is no length check for the entire
+// string s. I.e.  a domain name longer than 255 characters is considered valid.
 func IsDomainName(s string) (labels int, ok bool) {
 	_, labels, err := packDomainName(s, nil, 0, nil, false)
 	return labels, err == nil