Run following command could crash emacs:

cat <<END > test.el
    (progn (custom-set-variables
      '(face-font-family-alternatives
        '(("Monospace" "courier" "fixed")
          ("courier" "CMU Typewriter Text" "fixed")
          ("Sans Serif" "helv" "helvetica" "arial" "fixed")
          ("helv" "helvetica" "arial" "fixed"))))
       (char-displayable-p 215))
END
emacs -Q --load test.el

The face-font-family-alternatives value is taken from the default value.

`bt full` and `xbacktrace` attached.

In GNU Emacs 24.4.50.16 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.10)
 of 2014-06-30 on kanru-mozilla
Repository revision: 117446 rgm@gnu.org-20140630000151-7ofr4tf7tvev5alx
Windowing system distributor `The X.Org Foundation', version 11.0.11204000
System Description:	Debian GNU/Linux 7.5 (wheezy)