diff --git a/templates/base.html b/templates/base.html
index 26b3761..dbe4a31 100644
--- a/templates/base.html
+++ b/templates/base.html
@@ -81,7 +81,7 @@
   <link rel="stylesheet" type="text/css" href="{{ SITEURL }}/{{ THEME_STATIC_DIR }}/font-awesome/css/solid.css">
 
   {% if CUSTOM_CSS %}
-    <link rel="stylesheet" type="text/css" href="{{ SITEURL }}/{{ CUSTOM_CSS }}">
+  <link rel="stylesheet" type="text/css" href="{% if main_siteurl is defined %}{{ main_site }}{% else %}{{ SITEURL }}{% endif %}/{{ CUSTOM_CSS }}">
   {% endif %}
 
   {% if FEED_ALL_ATOM %}