diff --git a/src/enacl.erl b/src/enacl.erl
index 01fdd7e..e73e4b3 100644
--- a/src/enacl.erl
+++ b/src/enacl.erl
@@ -374,7 +374,7 @@ stream(_, _, _) -> error(badarg).
 %% @end
 -spec stream_xor(Msg, Nonce, Key) -> CipherText
   when
-    Msg :: binary(),
+    Msg :: iodata(),
     Nonce :: binary(),
     Key :: binary(),
     CipherText :: binary().