diff --git a/src/net/http/transport.go b/src/net/http/transport.go
index 47cb992a50..309194e8e5 100644
--- a/src/net/http/transport.go
+++ b/src/net/http/transport.go
@@ -427,6 +427,7 @@ func (t *Transport) onceSetNextProtoDefaults() {
 //
 // The environment values may be either a complete URL or a
 // "host[:port]", in which case the "http" scheme is assumed.
+// The schemes "http", "https", and "socks5" are supported.
 // An error is returned if the value is a different form.
 //
 // A nil URL and nil error are returned if no proxy is defined in the