diff --git a/lib/editor/components/timetable/CalendarSelect.js b/lib/editor/components/timetable/CalendarSelect.js
index 1b9eca235..73ff815ec 100644
--- a/lib/editor/components/timetable/CalendarSelect.js
+++ b/lib/editor/components/timetable/CalendarSelect.js
@@ -7,7 +7,7 @@ import Select from 'react-select'
 
 import * as activeActions from '../../actions/active'
 import {entityIsNew} from '../../util/objects'
-import type {Pattern, GtfsRoute, Feed, ServiceCalendar, ScheduleException, Trip, TripCounts} from '../../../types'
+import type {Pattern, GtfsRoute, Feed, ServiceCalendar, ScheduleExceptionCalendar, Trip, TripCounts} from '../../../types'
 
 type CalendarOption = {
   calendar: ServiceCalendar,
@@ -20,10 +20,10 @@ type CalendarOption = {
 }
 
 type Props = {
-  activeCalendar: ?ServiceCalendar,
+  activeCalendar: ?ServiceCalendar | ?ScheduleExceptionCalendar,
   activePattern: Pattern,
   calendars: Array<ServiceCalendar>,
-  exceptionBasedCalendars: Array<ScheduleException>,
+  exceptionBasedCalendars: ?Array<ScheduleExceptionCalendar>,
   feedSource: Feed,
   route: GtfsRoute,
   setActiveEntity: typeof activeActions.setActiveEntity,
diff --git a/lib/editor/util/timetable.js b/lib/editor/util/timetable.js
index ed1bed610..e184fc206 100644
--- a/lib/editor/util/timetable.js
+++ b/lib/editor/util/timetable.js
@@ -51,7 +51,7 @@ export function parseTime (timeString: string) {
 }
 
 // Helper function to find and return the active calendar, be it traditional or exception-based.
-export function getActiveCalendar (calendars: Array<ServiceCalendar>, exceptionBasedCalendars: Array<ScheduleExceptionCalendar>, activeScheduleId: string) {
+export function getActiveCalendar (calendars: Array<ServiceCalendar>, exceptionBasedCalendars: Array<ScheduleExceptionCalendar>, activeScheduleId: string): ?ServiceCalendar | ?ScheduleExceptionCalendar {
   const activeCalendarFilter = c => c.service_id === activeScheduleId
   return calendars.find(activeCalendarFilter) || exceptionBasedCalendars.find(activeCalendarFilter)
 }
diff --git a/lib/editor/util/validation.js b/lib/editor/util/validation.js
index 05139406d..a94e23b6a 100644
--- a/lib/editor/util/validation.js
+++ b/lib/editor/util/validation.js
@@ -340,6 +340,7 @@ export function validate (
         const calendars: Array<ServiceCalendar> = clone(getTableById(tableData, 'calendar'))
 
         // Check if service ID exists elsewhere
+        // $FlowFixMe: Array#some confuses flow it seems.
         if (entity.custom_schedule && calendars.some(c => c.service_id === entity.custom_schedule)) {
           const reason = messages('conflictingServiceId')
           valErrors.push(validationIssue(reason, messages('customServiceId')))