Scheduled transaction editor immediately crashes Gnucash

[javastead]

When attempting to edit my scheduled transactions by using the menu
"Actions" then "Scheduled Transactions" then "Scheduled Transactions
Editor", Gnucash crashes with the following error (when run from a
terminal):

** ERROR **: file gnc-dense-cal.c: line 319 (gnc_dense_cal_init):
assertion failed: (dcal->monthLabelFont)
aborting...
Aborted

The same occurs if running Gnucash on a new file.

Using Gnucash 1.8.11 on Gentoo.

It's been quite a while since I used the scheduled transaction editor,
so I don't know what change on the system might have caused this.

Any clues?