diff --git a/README.md b/README.md
index fab72d6..bbf8bdb 100644
--- a/README.md
+++ b/README.md
@@ -146,9 +146,13 @@ window.addEventListener('WebComponentsReady', function(e) {
 
 ## Known Issues
 
+  * [ShadowDOM CSS is not encapsulated out of the box](#shadycss)
   * [Custom element's constructor property is unreliable](#constructor)
   * [Contenteditable elements do not trigger MutationObserver](#contentedit)
   * [ShadyCSS: :host(.zot:not(.bar:nth-child(2))) doesn't work](#nestedparens)
+  
+### ShadowDOM CSS is not encapsulated out of the box <a id="shadycss"></a>
+The ShadowDOM polyfill is not able to encapsulate CSS in ShadowDOM out of the box. You need to use specific code from the ShadyCSS library, included with the polyfill. See [ShadyCSS instructions](https://github.com/webcomponents/shadycss).
 
 ### Custom element's constructor property is unreliable <a id="constructor"></a>
 See [#215](https://github.com/webcomponents/webcomponentsjs/issues/215) for background.