markup fix
diff --git a/Doc/ref/ref8.tex b/Doc/ref/ref8.tex
index d10c87f..78e7934 100644
--- a/Doc/ref/ref8.tex
+++ b/Doc/ref/ref8.tex
@@ -34,7 +34,7 @@
\index{interactive mode}
\refbimodindex{__main__}
-Under {\UNIX}, a complete program can be passed to the interpreter in
+Under \UNIX{}, a complete program can be passed to the interpreter in
three forms: with the \programopt{-c} \var{string} command line option, as a
file passed as the first command line argument, or as standard input.
If the file or standard input is a tty device, the interpreter enters