diff --git a/lib/libc/gen/gethostname.3 b/lib/libc/gen/gethostname.3
index 8596a2d1c05..ba0bbe3a1f2 100644
--- a/lib/libc/gen/gethostname.3
+++ b/lib/libc/gen/gethostname.3
@@ -93,6 +93,8 @@ Host names are limited to
 (from
 .Ao Pa sys/param.h Ac )
 characters, currently 256.
+This includes the trailing
+.Dv NUL .
 .Sh HISTORY
 The
 .Fn gethostname