diff --git a/gnu/usr.bin/groff/tmac/mdoc.local b/gnu/usr.bin/groff/tmac/mdoc.local
index c96984319bf3..bfcb654c625f 100644
--- a/gnu/usr.bin/groff/tmac/mdoc.local
+++ b/gnu/usr.bin/groff/tmac/mdoc.local
@@ -69,6 +69,7 @@
 .
 .\" FreeBSD releases not found in doc-common
 .ds doc-operating-system-FreeBSD-6.3    6.3
+.ds doc-operating-system-FreeBSD-6.4    6.4
 .ds doc-operating-system-FreeBSD-7.1    7.1
 .ds doc-operating-system-FreeBSD-8.0    8.0
 .