Fails to load on LispWorks due to Unicode in README.md

[Zulu-Inuoe]

When loading on LispWorks 6.1 x86 on Windows I get

Error: Error while trying to load definition for system jonathan from pathname C:\Users\zulu\quicklisp\dists\quicklisp\software\jonathan-20190202-git\jonathan.asd:
          External format (:UTF-8 :EOL-STYLE :LF) got error reading #<STREAM::EF-FILE-STREAM C:\Users\zulu\quicklisp\dists\quicklisp\software\jonathan-20190202-git\README.md>: cannot convert #x2000B to a character as this exceeds the char-code-limit (#x10000).

Tracked this down to the system doing a read-time eval to load in the readme into its long-description:

:long-description
  #.(with-open-file (stream (merge-pathnames
                             #p"README.md"
                             (or *load-pathname* *compile-file-pathname*))
                            :if-does-not-exist nil
                            :direction :input
                            :element-type #+lispworks :default #-lispworks 'character
                            :external-format #+clisp charset:utf-8 #-clisp :utf-8)