diff --git a/tls.go b/tls.go
index dfde010..24af6ec 100644
--- a/tls.go
+++ b/tls.go
@@ -443,6 +443,7 @@ func NewListener(inner net.Listener, config *Config) net.Listener {
 // The configuration config must be non-nil and must include
 // at least one certificate or else set GetCertificate.
 func Listen(network, laddr string, config *Config) (net.Listener, error) {
+	// If this condition changes, consider updating http.Server.ServeTLS too.
 	if config == nil || len(config.Certificates) == 0 &&
 		config.GetCertificate == nil && config.GetConfigForClient == nil {
 		return nil, errors.New("tls: neither Certificates, GetCertificate, nor GetConfigForClient set in Config")