/ mounted read-only after error in /etc/rc.conf

[Pieter Donche]

I made a typing error when chanign /etc/rc.conf
(linux_enable=YES")
when rebooting the system, the boot stops
/etc/rc.conf: 22: Syntax error: Unterminated quote string
Enter full pathname of shell or RETURN for /bin/sh:
#
this leaves me with
/dev/ds0s1a on / (ufs, local, read-only)

since / is read-only I can not edit /etc/rc.conf to correct the error.

How to solve this?