diff --git a/gnu/usr.bin/groff/tmac/mdoc.local b/gnu/usr.bin/groff/tmac/mdoc.local
index 4c83635c503..a3073ff7d8d 100644
--- a/gnu/usr.bin/groff/tmac/mdoc.local
+++ b/gnu/usr.bin/groff/tmac/mdoc.local
@@ -75,6 +75,7 @@
 .ds doc-operating-system-FreeBSD-7.2    7.2
 .ds doc-operating-system-FreeBSD-7.3    7.3
 .ds doc-operating-system-FreeBSD-8.0    8.0
+.ds doc-operating-system-FreeBSD-8.1    8.1
 .ds doc-operating-system-FreeBSD-9.0    9.0
 .
 .\" Definitions not (yet) in doc-syms