diff --git a/program/include/rcube_addressbook.php b/program/include/rcube_addressbook.php
index f4f255322..892ae263a 100644
--- a/program/include/rcube_addressbook.php
+++ b/program/include/rcube_addressbook.php
@@ -434,6 +434,11 @@ abstract class rcube_addressbook
             }
         }
 
+        // remove duplicates
+        if ($flat && !empty($out)) {
+            $out = array_unique($out);
+        }
+
         return $out;
     }