diff --git a/services/backend/src/routes/courses.ts b/services/backend/src/routes/courses.ts
index fd600ef85..594179ecb 100644
--- a/services/backend/src/routes/courses.ts
+++ b/services/backend/src/routes/courses.ts
@@ -12,7 +12,12 @@ import {
 import type { CourseWithSubsId } from '@oodikone/shared/types/course'
 import { getCourseYearlyStats } from '../services/courses'
 import { getCoursesByNameAndOrCode } from '../services/courses/courseFinders'
-import { getFullStudyProgrammeRights, hasFullAccessToStudentData, validateParamLength } from '../util'
+import {
+  getFullStudyProgrammeRights,
+  handleQueryArrays,
+  hasFullAccessToStudentData,
+  validateParamLength,
+} from '../util'
 
 const router = Router()
 
@@ -53,7 +58,9 @@ router.get<never, CanError<CourseYearlyStatsResBody>, CourseYearlyStatsReqBody,
   async (req, res) => {
     const { codes, combineSubstitutions, separate } = req.query
 
-    if (!codes) {
+    const courseCodes = handleQueryArrays(codes)
+
+    if (!courseCodes) {
       return res.status(422).send({ error: 'Missing required query parameters' })
     }
 
@@ -75,7 +82,7 @@ router.get<never, CanError<CourseYearlyStatsResBody>, CourseYearlyStatsReqBody,
     const useCombineSubstitutions = combineSubstitutions !== 'false'
     const useSeparate = separate === 'true'
 
-    const results = await getCourseYearlyStats(codes, useSeparate, anonymizationSalt, useCombineSubstitutions)
+    const results = await getCourseYearlyStats(courseCodes, useSeparate, anonymizationSalt, useCombineSubstitutions)
     res.json(results)
   }
 )
diff --git a/services/backend/src/routes/population.ts b/services/backend/src/routes/population.ts
index 54c76a3ad..186a67ad4 100644
--- a/services/backend/src/routes/population.ts
+++ b/services/backend/src/routes/population.ts
@@ -26,7 +26,7 @@ import { parseDateRangeFromParams } from '../services/populations/shared'
 import { statisticsOf } from '../services/populations/statisticsOf'
 import { getStudentNumbersWithStudyRights } from '../services/populations/studentNumbersWithStudyRights'
 import { findByCourseAndSemesters } from '../services/students'
-import { getFullStudyProgrammeRights, hasFullAccessToStudentData } from '../util'
+import { getFullStudyProgrammeRights, handleQueryArrays, hasFullAccessToStudentData } from '../util'
 
 const router = Router()
 
@@ -103,10 +103,6 @@ router.get<never, CanError<PopulationstatisticsResBody>, PopulationstatisticsReq
     const { id: userId, roles: userRoles, programmeRights: userProgrammeRights, studentsUserCanAccess } = req.user
     const { programme, combinedProgramme } = req.query
 
-    // NOTE: Make sure we have only arrays, "/...&years=2021" is parsed by express as years: 2021, not [2021]
-    const handleQueryArrays = <T>(requestField: T | T[]): T[] => {
-      return Array.isArray(requestField) ? requestField : [requestField]
-    }
     const years = handleQueryArrays(req.query.years)
     const semesters = handleQueryArrays(req.query.semesters)
     const studentStatuses = handleQueryArrays(req.query.studentStatuses) // NOTE: TRANSFERRED means transferred out of the program
diff --git a/services/backend/src/util/index.ts b/services/backend/src/util/index.ts
index 3789479ed..842035bb7 100644
--- a/services/backend/src/util/index.ts
+++ b/services/backend/src/util/index.ts
@@ -100,3 +100,8 @@ export const safeJSONParse = async <T>(json: string): Promise<T | null> => {
 
   return data
 }
+
+// NOTE: Make sure we have only arrays, "/...&years=2021" is parsed by express as years: 2021, not [2021]
+export const handleQueryArrays = <T>(requestField: T | T[]): T[] => {
+  return Array.isArray(requestField) ? requestField : [requestField]
+}