diff --git a/lib/libc/gen/err.3 b/lib/libc/gen/err.3
index f9fcdaff141b..8bd31c360e11 100644
--- a/lib/libc/gen/err.3
+++ b/lib/libc/gen/err.3
@@ -217,7 +217,9 @@ The
 .Fn err
 and
 .Fn warn
-families of functions are BSD extensions.
+families of functions are
+.Bx
+extensions.
 As such they should not be used in truly portable code.
 Use
 .Fn strerror