diff --git a/doc/_static/default2.css b/doc/_static/default2.css
index e5ebaf98..d63d81f8 100644
--- a/doc/_static/default2.css
+++ b/doc/_static/default2.css
@@ -1,4 +1,4 @@
-@import url(http://fonts.googleapis.com/css?family=Roboto:400,400italic,500,500italic);
+@import url(//fonts.googleapis.com/css?family=Roboto:400,400italic,500,500italic);
 
 pre, tt {
     font-family:  monospace, sans-serif;