diff --git a/_includes/nav.html b/_includes/nav.html
index 4adb5480c..4191b0bc6 100644
--- a/_includes/nav.html
+++ b/_includes/nav.html
@@ -1,4 +1,4 @@
-<nav id="mainNav" class="navbar navbar-default navbar-fixed-top">
+<nav id="mainNav" class="navbar navbar-default navbar-fixed-top affix-top">
     <div class="container">
         <!-- Brand and toggle get grouped for better mobile display -->
         <div class="navbar-header">