diff --git a/src/lib/builtins.pl b/src/lib/builtins.pl
index 3c9c27a1..1a92acf9 100644
--- a/src/lib/builtins.pl
+++ b/src/lib/builtins.pl
@@ -1429,7 +1429,10 @@ parse_stream_options(Options, OptionValues, Stub) :-
 
 
 parse_stream_options_(type(Type), type-Type) :-
-    (  nonvar(Type), lists:member(Type, [text, binary]), !, true
+    (  var(Type) ->
+       throw(error(instantiation_error, open/4)) % 8.1.3 7)
+    ;
+       lists:member(Type, [text, binary]) -> true
     ;
        throw(error(domain_error(stream_option, type(Type)), _))
     ).