diff --git a/data/config.default.php b/data/config.default.php
index c850521..9c2f7f3 100644
--- a/data/config.default.php
+++ b/data/config.default.php
@@ -81,13 +81,15 @@ $theme = 'default';
 
 /**
  * SemanticScuttle root directory.
- *
  * Set to NULL to autodetect the root url of the website.
  *
  * If your installation is in a subdirectory like
  * "http://www.example.com/semanticscuttle/" then
  * replace NULL by your address (between "" and with trailing '/')
  *
+ * The autodetection works for both HTTP and HTTPS urls.
+ * If you offer HTTP *only*, then set your root url here.
+ *
  * @var string
  */
 $root = null;
diff --git a/doc/ChangeLog b/doc/ChangeLog
index 860a213..b7bf843 100644
--- a/doc/ChangeLog
+++ b/doc/ChangeLog
@@ -7,6 +7,7 @@ ChangeLog for SemantiScuttle
 -------------------
 - Fix bug #3385724: Rename tag ends with XML Parsing Error
 - Fix bug #3386178: "system:unfiled" secret tag does not work
+- Fix bug #3384416: Update documentation to explain HTTP/HTTPS root problem
 
 Run ``scripts/fix-unfiled-tags.php`` to fix old bookmarks that miss the
 ``system:unfiled`` tags.
diff --git a/doc/configuration.rst b/doc/configuration.rst
index f457ebb..c34318a 100644
--- a/doc/configuration.rst
+++ b/doc/configuration.rst
@@ -56,3 +56,24 @@ per-host configuration files:
 - ``data/config.$hostname.php``
 - ``/etc/semanticscuttle/config.$hostname.php``
 
+
+
+Configuration options
+=====================
+``$root`` URL
+-------------
+Normally, this configuration setting is detected automatically and will
+work for both HTTP and HTTPS installations.
+
+If your installation is available on **HTTP only**, then you need to configure
+it.
+
+The value is the full URL to your installation, including a trailing
+slash::
+
+    $root = "http://homepage.example.org/semanticscuttle/";
+
+or::
+
+    $root = "http://bookmarks.example.org/";
+