Removing an alerting channel fails

Attempting to remove a value from alert_email_addresses in a project using this module gives the following error:

│ Error: Error when reading or editing NotificationChannel: googleapi: Error 400: Could not delete "projects/webcms-devel-0d699960/notificationChannels/9093485665884039924" because it is still being referenced by: "projects/webcms-devel-0d699960/alertPolicies/2942458646498042898", "projects/webcms-devel-0d699960/alertPolicies/4689098891948536408"