diff --git a/README.rst b/README.rst
index a5d3af45..8bd4cd5c 100644
--- a/README.rst
+++ b/README.rst
@@ -56,6 +56,10 @@ In order to plug in ``aiohttp_debugtoolbar``, call
     app = web.Application(loop=loop)
     aiohttp_debugtoolbar.setup(app)
 
+Note:
+
+  This middleware needs a response that contains a valid HTML document to work.(i.e. *content_type: 'text/html'* and contains *</head>* and *</body>* tags.)
+
 
 Full Example
 ------------