diff --git a/doc/css/gfm-mod.css b/doc/css/gfm-mod.css
index 5cd333d7a9..29518d3836 100644
--- a/doc/css/gfm-mod.css
+++ b/doc/css/gfm-mod.css
@@ -1062,6 +1062,7 @@ div#sidebar {
   top: 5px;
   min-width: 200px;
   font-size: 90%;
+  max-width: 15.1515%;
 }
 
 div#sidebar ul {