Index: /trunk/ccl/lib/nfcomp.lisp
===================================================================
--- /trunk/ccl/lib/nfcomp.lisp	(revision 6206)
+++ /trunk/ccl/lib/nfcomp.lisp	(revision 6207)
@@ -900,5 +900,5 @@
 (defvar *make-load-form-hash*)
 
-;Return a hash table containing subexp's which are referenced more than once.
+;;;Return a hash table containing subexp's which are referenced more than once.
 (defun fasl-scan (forms)
   (let* ((*fasdump-hash* (make-hash-table :size (length forms)          ; Crude estimate
@@ -986,5 +986,5 @@
                                  (ash 1 x8664::fulltag-immheader-2))))
            (case type-code
-             ((#.target::subtag-macptr #.target::subtag-dead-macptr) (fasl-unknown exp))
+             ((#.target::subtag-macptr #.target::subtag-dead-macptr) (unless (%null-ptr-p exp) (fasl-unknown exp)))
              (t (fasl-scan-ref exp)))
            (case type-code