diff --git a/phpgwapi/inc/class.groupdav_principals.inc.php b/phpgwapi/inc/class.groupdav_principals.inc.php
index f4a8813a7b..d7cf315794 100644
--- a/phpgwapi/inc/class.groupdav_principals.inc.php
+++ b/phpgwapi/inc/class.groupdav_principals.inc.php
@@ -991,9 +991,31 @@ class groupdav_principals extends groupdav_handler
 
 		$displayname = translation::convert($resource['name'],	translation::charset(), 'utf-8');
 
-		return ($is_location ? 'locations/' : 'resources/').$resource['res_id'].'-'.str_replace(array(' ','/',':','#','?'),'-',$displayname);
+		return ($is_location ? 'locations/' : 'resources/').$resource['res_id'].'-'.
+			preg_replace('/[^a-z0-9]+/i','-', self::to_ascii($resource['name']));
 	}
 
+	/**
+	 * Transliterate utf-8 filename to ascii, eg. 'Äpfel' --> 'Aepfel'
+	 *
+	 * @param string $str
+	 * @return string
+	 */
+	protected function to_ascii($str)
+	{
+		static $extra = array(
+			'ß' => 'ss',
+		);
+		$str = htmlentities($str,ENT_QUOTES,translation::charset());
+		$str = str_replace(array_keys($extra),array_values($extra),$str);
+		$str = preg_replace('/&([aAuUoO])uml;/','\\1e',$str);	// replace german umlauts with the letter plus one 'e'
+		$str = preg_replace('/&([a-zA-Z])(grave|acute|circ|ring|cedil|tilde|slash|uml);/','\\1',$str);	// remove all types of acents
+		$str = preg_replace('/&([a-zA-Z]+|#[0-9]+|);/','',$str);	// remove all other entities
+
+		return $str;
+	}
+
+
 	/**
 	 * Check if resource is a location
 	 *