COMPILE-FILE-ERROR while compiling parenscript package in 20.4.24

I reproduced this on both x64 and armv5. Loading src/special-operators.lisp from Parenscript-2.7.1 fails with:

;;; Internal error:
;;;   in file special-operators.lisp, position 10438
;;;   at (defun return-result-of ...)
;;;   ** Cannot coerce string TAG₁ to a base-string
Condition of type: COMPILE-FILE-ERROR

To reproduce just quickload parenscript. In ECL 16.1.3 I have used parenscript without issue.