diff --git a/index.html b/index.html
index 1cf3c4151..f3e6a30b7 100644
--- a/index.html
+++ b/index.html
@@ -676,7 +676,9 @@ jQuery('#underscore_button').bind('click', buttonView.onClick);
         Memoizes a given <b>function</b> by caching the computed result. Useful
         for speeding up slow-running computations. If passed an optional 
         <b>hashFunction</b>, it will be used to compute the hash key for storing
-        the result, based on the arguments to the original function.
+        the result, based on the arguments to the original function. The default
+        <b>hashFunction</b> just uses the first argument to the memoized function
+        as the key.
       </p>
       <pre>
 var fibonacci = function(n) {