Strange message or wrong errno on mismatching versions of plugin and server

An attempt to install ha_tokudb.so (from 5.5.33) on 5.5.32 server causes an error message which seems a tiny bit wrong:

MariaDB [(none)]> install soname 'ha_tokudb';

ERROR 1126 (HY000): Can't open shared library 'ha_tokudb.so' (errno: 0 API version for STORAGE ENGINE plugin TokuDB not supported by this version of the server)

The text itself is fine, but the "errno: 0 API version" part looks strange. Either 0 is the errno, or it refers to the API version – all the same, it doesn't seem quite right.