diff --git a/man4/ttyS.4 b/man4/ttyS.4
index 5ba50225a..9043f2564 100644
--- a/man4/ttyS.4
+++ b/man4/ttyS.4
@@ -42,7 +42,7 @@ chown root:tty /dev/ttyS[0\-3]
 .EE
 .in
 .SH FILES
-/dev/ttyS[0\-3]
+.I /dev/ttyS[0\-3]
 .SH SEE ALSO
 .BR chown (1),
 .BR mknod (1),