segfault from backtrace of do () with unbound variable

[Bill Schottstaedt]

guile> (version)
"1.4"
guile> (define hi (lambda (a) (do () ((> a 6)) (set! a ho))))
guile> (hi 2)
standard input:1:41: In expression (set! a ho):
standard input:1:41: Unbound variable: ho
ABORT: (unbound-variable)

Type "(backtrace)" to get more information or "(debug)" to enter the debugger.
guile> (backtrace)

Backtrace:
0* [hi 2]
1  Segmentation fault (core dumped)