:: doesn't work on macro expansion

Index: lib/utils/mu-readline.cc
--- lib/utils/mu-readline.cc.orig
+++ lib/utils/mu-readline.cc
@@ -74,7 +74,7 @@ Mu::have_readline()
 void
 Mu::setup_readline(const std::string& histpath, size_t maxlines)
 {
-	is_a_tty  = !!::isatty(::fileno(stdout));
+	is_a_tty  = !!::isatty(fileno(stdout));
 	hist_path = histpath;
 	max_lines = maxlines;