diff --git a/src/ejabberd_xmlrpc.erl b/src/ejabberd_xmlrpc.erl
index c3b2fdab7..b59001819 100644
--- a/src/ejabberd_xmlrpc.erl
+++ b/src/ejabberd_xmlrpc.erl
@@ -448,8 +448,8 @@ format_arg({array, Elements}, {list, ElementsDef})
 format_arg(Arg, integer) when is_integer(Arg) -> Arg;
 format_arg(Arg, binary) when is_list(Arg) -> list_to_binary(Arg);
 format_arg(Arg, binary) when is_binary(Arg) -> Arg;
-format_arg(Arg, string) when is_list(Arg) -> list_to_binary(Arg);
-format_arg(Arg, string) when is_binary(Arg) -> Arg;
+format_arg(Arg, string) when is_list(Arg) -> Arg;
+format_arg(Arg, string) when is_binary(Arg) -> binary_to_list(Arg);
 format_arg(Arg, Format) ->
     ?ERROR_MSG("don't know how to format Arg ~p for format ~p", [Arg, Format]),
     throw({error_formatting_argument, Arg, Format}).