diff --git a/en_US.ISO8859-1/books/design-44bsd/book.xml b/en_US.ISO8859-1/books/design-44bsd/book.xml
index 2b07856399..e10c97d71f 100644
--- a/en_US.ISO8859-1/books/design-44bsd/book.xml
+++ b/en_US.ISO8859-1/books/design-44bsd/book.xml
@@ -1961,7 +1961,7 @@
     in addition to the natural desire of users
     to give files long descriptive names,
     a common way of forming filenames is as
-      <filename>basename.extension</filename>,
+      <filename><replaceable>basename</replaceable>.<replaceable>extension</replaceable></filename>,
     where the extension (indicating the kind of file, such as
     <literal>.c</literal>
     for C source or