diff --git a/spice_auto.html b/spice_auto.html
index 81ec8cf..0a01996 100644
--- a/spice_auto.html
+++ b/spice_auto.html
@@ -85,7 +85,20 @@
 
                 // By default, use the host and port of server that served this file
                 host = spice_query_var('host', window.location.hostname);
-                port = spice_query_var('port', window.location.port);
+
+                // Note that using the web server port only makes sense
+                //  if your web server has a reverse proxy to relay the WebSocket
+                //  traffic to the correct destination port.
+                var default_port = window.location.port;
+                if (!default_port) {
+                    if (window.location.protocol == 'http:') {
+                        default_port = 80;
+                    }
+                    else if (window.location.protocol == 'https:') {
+                        default_port = 443;
+                    }
+                }
+                port = spice_query_var('port', default_port);
 
                 // If a token variable is passed in, set the parameter in a cookie.
                 // This is used by nova-spiceproxy.