diff --git a/client.go b/client.go
index c4b62fbc..e4fc18f7 100644
--- a/client.go
+++ b/client.go
@@ -48,6 +48,8 @@ func NewClient(netConn net.Conn, u *url.URL, requestHeader http.Header, readBufS
 }
 
 // A Dialer contains options for connecting to WebSocket server.
+//
+// It is safe to call Dialer's methods concurrently.
 type Dialer struct {
 	// NetDial specifies the dial function for creating TCP connections. If
 	// NetDial is nil, net.Dial is used.
diff --git a/server.go b/server.go
index 152ebf89..406f3076 100644
--- a/server.go
+++ b/server.go
@@ -23,6 +23,8 @@ func (e HandshakeError) Error() string { return e.message }
 
 // Upgrader specifies parameters for upgrading an HTTP connection to a
 // WebSocket connection.
+//
+// It is safe to call Upgrader's methods concurrently.
 type Upgrader struct {
 	// HandshakeTimeout specifies the duration for the handshake to complete.
 	HandshakeTimeout time.Duration