diff --git a/gnu/usr.bin/groff/tmac/mdoc.local b/gnu/usr.bin/groff/tmac/mdoc.local
index 447cf3bc7496..0dc60a3e323e 100644
--- a/gnu/usr.bin/groff/tmac/mdoc.local
+++ b/gnu/usr.bin/groff/tmac/mdoc.local
@@ -65,6 +65,7 @@
 .ds doc-operating-system-FreeBSD-5.4    5.4
 .ds doc-operating-system-FreeBSD-5.5    5.5
 .ds doc-operating-system-FreeBSD-6.0    6.0
+.ds doc-operating-system-FreeBSD-6.1    6.1
 .ds doc-operating-system-FreeBSD-7.0    7.0
 .
 .ec