diff --git a/src/lib/os.pl b/src/lib/os.pl
index 152077ae..8b0087a4 100644
--- a/src/lib/os.pl
+++ b/src/lib/os.pl
@@ -137,7 +137,9 @@ raw_argv(Argv) :-
 argv(Argv) :-
     can_be(list, Argv),
     '$argv'(Argv0),
-    (    append(Argv1, ["--"|Argv], Argv0) ->
-         \+ member("--", Argv1)
-    ;    Argv = []
+    ( member("--", Argv0) ->
+        append(Argv1, ["--"|Argv], Argv0),
+        \+ member("--", Argv1)
+    ;
+        Argv = []
     ).