diff --git a/templates/nginx.conf.tmpl b/templates/nginx.conf.tmpl
index 3085323..deb2985 100644
--- a/templates/nginx.conf.tmpl
+++ b/templates/nginx.conf.tmpl
@@ -131,5 +131,14 @@ http {
         ~^/(?<no_slash>.*)$ $no_slash;
     }
 
+    # http://nginx.org/en/docs/http/websocket.html
+    # top-level http config for websocket headers
+    # If Upgrade is defined, Connection = upgrade
+    # If Upgrade is empty, Connection = close
+    map $http_upgrade $connection_upgrade {
+        default upgrade;
+        ''      close;
+    }
+
     include {{ getenv "NGINX_CONF_INCLUDE" "conf.d/*.conf" }};
 }