diff --git a/share/man/man9/devclass.9 b/share/man/man9/devclass.9
index 003c63d87ff5..4f0eec6659af 100644
--- a/share/man/man9/devclass.9
+++ b/share/man/man9/devclass.9
@@ -48,6 +48,10 @@ Each
 has a name and there cannot be two devclasses with the same name.
 This ensures that unique unit numbers are allocated to device
 instances.
+.Pp
+Beware that this means
+.Dv devclass
+must be the same for different bus attachments of the same device driver.
 .Sh SEE ALSO
 .Xr devclass_add_driver 9 ,
 .Xr devclass_delete_driver 9 ,