diff --git a/addressbook/inc/class.addressbook_groupdav.inc.php b/addressbook/inc/class.addressbook_groupdav.inc.php
index 35c936ea57..85ae60ef3b 100644
--- a/addressbook/inc/class.addressbook_groupdav.inc.php
+++ b/addressbook/inc/class.addressbook_groupdav.inc.php
@@ -735,9 +735,7 @@ class addressbook_groupdav extends groupdav_handler
 	{
 		if (!isset($modified)) $modified = $this->getctag($path, $user);
 
-		return (strpos($this->base_uri, 'http') === 0 ? '' :	// need a full uri, not just a path
-				($_SERVER["HTTPS"] === "on" ? "https:" : "http:") .'//' . $_SERVER['HTTP_HOST']).
-			$this->base_uri.$path.$modified;
+		return $this->base_uri().$path.$modified;
 	}
 
 	/**
diff --git a/phpgwapi/inc/class.groupdav_handler.inc.php b/phpgwapi/inc/class.groupdav_handler.inc.php
index 7c592ea9ae..76b9ed458d 100644
--- a/phpgwapi/inc/class.groupdav_handler.inc.php
+++ b/phpgwapi/inc/class.groupdav_handler.inc.php
@@ -551,6 +551,34 @@ abstract class groupdav_handler
 		// we urldecode here, as HTTP_WebDAV_Server uses a minimal (#?%) urlencoding for incomming pathes and urlencodes pathes in propfind
 		return $this->groupdav->add_resource($path.urldecode($this->get_path($entry)), $props, $privileges);
 	}
+
+	/**
+	 * Return base uri, making sure it's either a full uri (incl. protocoll and host) or just a path
+	 *
+	 * base_uri of WebDAV class can be both, depending on EGroupware config
+	 *
+	 * @param boolean $full_uri=true
+	 * @return string eg. https://domain.com/egroupware/groupdav.php
+	 */
+	public function base_uri($full_uri=true)
+	{
+		static $uri;
+		static $path;
+
+		if (!isset($uri))
+		{
+			$uri = $path = $this->groupdav->base_uri;
+			if ($uri[0] == '/')
+			{
+				$uri = ($_SERVER["HTTPS"] === "on" ? "https:" : "http:") .'//' . $_SERVER['HTTP_HOST'] . $uri;
+			}
+			else
+			{
+				$path = parse_url($uri, PHP_URL_PATH);
+			}
+		}
+		return $full_uri ? $uri : $path;
+	}
 }
 
 /**
diff --git a/phpgwapi/inc/class.groupdav_principals.inc.php b/phpgwapi/inc/class.groupdav_principals.inc.php
index aed7d19cbc..37120313a7 100644
--- a/phpgwapi/inc/class.groupdav_principals.inc.php
+++ b/phpgwapi/inc/class.groupdav_principals.inc.php
@@ -937,8 +937,10 @@ class groupdav_principals extends groupdav_handler
 				HTTP_WebDAV_Server::mkprop('href',$this->base_uri.'/'.$account['account_lid'].'/inbox/'))),
 			'calendar-user-address-set' => HTTP_WebDAV_Server::mkprop(groupdav::CALDAV,'calendar-user-address-set',array(
 				HTTP_WebDAV_Server::mkprop('href','MAILTO:'.$account['account_email']),
+				HTTP_WebDAV_Server::mkprop('href',$this->base_uri(true).'/principals/users/'.$account['account_lid'].'/'),
+				HTTP_WebDAV_Server::mkprop('href',$this->base_uri(false).'/principals/users/'.$account['account_lid'].'/'),
 				HTTP_WebDAV_Server::mkprop('href','urn:uuid:'.common::generate_uid('accounts', $account['account_id'])),
-				HTTP_WebDAV_Server::mkprop('href',$this->base_uri.'/principals/users/'.$account['account_lid'].'/'))),
+			)),
 			'calendar-user-type' => HTTP_WebDAV_Server::mkprop(groupdav::CALDAV,'calendar-user-type','INDIVIDUAL'),
 			// Calendarserver
 			'email-address-set' => HTTP_WebDAV_Server::mkprop(groupdav::CALENDARSERVER,'email-address-set',array(
@@ -1093,8 +1095,10 @@ class groupdav_principals extends groupdav_handler
 			'addressbook-home-set' => HTTP_WebDAV_Server::mkprop(groupdav::CARDDAV,'addressbook-home-set',array(
 				HTTP_WebDAV_Server::mkprop('href',$this->base_uri.'/'.$account['account_lid'].'/'))),
 			'calendar-user-address-set' => HTTP_WebDAV_Server::mkprop(groupdav::CALDAV,'calendar-user-address-set',array(
+				HTTP_WebDAV_Server::mkprop('href',$this->base_uri(true).'/principals/groups/'.$account['account_lid'].'/'),
+				HTTP_WebDAV_Server::mkprop('href',$this->base_uri(false).'/principals/groups/'.$account['account_lid'].'/'),
 				HTTP_WebDAV_Server::mkprop('href','urn:uuid:'.common::generate_uid('accounts', $account['account_id'])),
-				HTTP_WebDAV_Server::mkprop('href',$this->base_uri.'/principals/groups/'.$account['account_lid'].'/'))),
+			)),
 			'record-type' => HTTP_WebDAV_Server::mkprop(groupdav::CALENDARSERVER,'record-type','groups'),
 			'calendar-user-type' => HTTP_WebDAV_Server::mkprop(groupdav::CALDAV,'calendar-user-type','GROUP'),
 			'group-member-set' => $this->principal_set('group-member-set', $groupmembers),
@@ -1117,8 +1121,10 @@ class groupdav_principals extends groupdav_handler
 			'getetag' => $this->get_resource_etag($resource),
 			'displayname' => $displayname,
 			'calendar-user-address-set' => HTTP_WebDAV_Server::mkprop(groupdav::CALDAV,'calendar-user-address-set',array(
+				HTTP_WebDAV_Server::mkprop('href',$this->base_uri(true).'/principals/'.$name.'/'),
+				HTTP_WebDAV_Server::mkprop('href',$this->base_uri(false).'/principals/'.$name.'/'),
 				HTTP_WebDAV_Server::mkprop('href','urn:uuid:'.common::generate_uid('resources', $resource['res_id'])),
-				HTTP_WebDAV_Server::mkprop('href',$this->base_uri.'/principals/'.$name.'/'))),
+			)),
 			'record-type' => HTTP_WebDAV_Server::mkprop(groupdav::CALENDARSERVER,'record-type',$is_location ? 'locations' : 'resources'),
 			'calendar-user-type' => HTTP_WebDAV_Server::mkprop(groupdav::CALDAV,'calendar-user-type',$is_location ? 'ROOM' : 'RESOURCE'),
 			'resource-id' => array(HTTP_WebDAV_Server::mkprop('href','urn:uuid:'.common::generate_uid('resources', $resource['res_id']))),