seg fault

Segmentation fault. Attempted to access resticted memory address #x7F438B9AF000.

This is due either to a problem in foreign code (e.g., C++), or a bug in Clasp itself.
   [Condition of type EXT:SEGMENTATION-VIOLATION]

Restarts:
 0: [TRY-RECOMPILING] Recompile reader and try loading it again
 1: [RETRY] Retry loading FASL for #<CL-SOURCE-FILE "fset" "Code" "reader">.
 2: [ACCEPT] Continue, treating loading FASL for #<CL-SOURCE-FILE "fset" "Code" "reader"> as having been successful.
 3: [RETRY] Retry ASDF operation.
 4: [CLEAR-CONFIGURATION-AND-RETRY] Retry ASDF operation after resetting the configuration.
 5: [RETRY] Retry ASDF operation.
 --more--

Backtrace:
  0: (UNIVERSAL-ERROR-HANDLER NIL EXT:SEGMENTATION-VIOLATION (:ADDRESS 139928081723392))
  1: (ERROR EXT:SEGMENTATION-VIOLATION :ADDRESS 139928081723392)
  2: (SEGMENTATION-VIOLATION 139928081723392)
  3: (NON-LOWERCASE-CODE-CHAR)
  4: (LAMBDA)
  5: (MERGE-READTABLES-INTO)
  6: RUN-ALLmodule1247
  7: (LOAD)
  8: (LAMBDA)
  9: (CALL-WITH-MUFFLED-CONDITIONS #P"/home/sly/.cache/common-lisp/clasp-cclasp-boehm-0.4.2-2153-g2ab66ac26-cst-linux-x64/home/sly/projects/fset/Code/reader.fasp")
 10: (CALL-WITH-MUFFLED-LOADER-CONDITIONS)
 11: (LOAD*)
 12: (PERFORM-LISP-LOAD-FASL)
 13: ((METHOD PERFORM ((LOAD-OP CL-SOURCE-FILE))))
 14: (FUNCALL)
 15: LAMBDA
 16: (LAMBDA)
 17: (LAMBDA)
 18: (CALL-WITH-ASDF-SESSION)
 19: (CALL-WHILE-VISITING-ACTION)
 --more--