diff --git a/mail/inc/class.mail_compose.inc.php b/mail/inc/class.mail_compose.inc.php
index 3522543eb2..a7ce875b71 100644
--- a/mail/inc/class.mail_compose.inc.php
+++ b/mail/inc/class.mail_compose.inc.php
@@ -2849,7 +2849,7 @@ class mail_compose
 				}
 			}
 		}
-		return array_values(array_merge($_emailAddressList, $addrFromList));
+		return array_values(array_merge((array)$_emailAddressList, $addrFromList));
 	}
 
 	/**