diff --git a/jls/lang/luv_async.lua b/jls/lang/luv_async.lua
index 2073877..5e1e460 100644
--- a/jls/lang/luv_async.lua
+++ b/jls/lang/luv_async.lua
@@ -29,7 +29,10 @@ return function(value)
       return setmetatable({
         _cleanmt = false,
         _metatable = mt,
-        _data = value
+        _data = value,
+        close = function()
+          error('cannot close async argument')
+        end
       }, ASYNC_MT)
     end
   end
diff --git a/jls/net/http/HttpExchange.lua b/jls/net/http/HttpExchange.lua
index e7ddb4d..379dc0c 100644
--- a/jls/net/http/HttpExchange.lua
+++ b/jls/net/http/HttpExchange.lua
@@ -241,6 +241,7 @@ end, function(HttpExchange)
     json = 'application/json',
     htm = 'text/html',
     html = 'text/html',
+    xhtml = 'application/xhtml+xml',
     mp4 = 'video/mp4',
     svg = 'image/svg+xml',
     txt = 'text/plain',