diff --git a/src/app/events/services/test-state.service.ts b/src/app/events/services/test-state.service.ts
index 1fef9dff7..0b4621b3b 100644
--- a/src/app/events/services/test-state.service.ts
+++ b/src/app/events/services/test-state.service.ts
@@ -4,6 +4,7 @@ import {
   combineLatest,
   merge,
   Observable,
+  of,
   ReplaySubject,
   scan,
   shareReplay,
@@ -123,18 +124,22 @@ export class TestStateService {
     this.gradingScaleIds$
   );
 
+  private UNDEFINED_GRADINGSCALE_ID = -1;
   private gradingScalesOptions$: Observable<GradingScaleOptions> = this.gradingScales$.pipe(
     map((gradingScales) =>
       gradingScales
         .map((gradingScale) => {
-          return {
-            id: gradingScale.Id,
-            options: gradingScale.Grades.map((gradeOption) => {
+          const id = gradingScale?.Id || this.UNDEFINED_GRADINGSCALE_ID;
+          const options =
+            gradingScale?.Grades.map((gradeOption) => {
               return {
                 Key: gradeOption.Id,
                 Value: gradeOption.Designation,
               };
-            }),
+            }) || [];
+          return {
+            id,
+            options,
           };
         })
         .reduce(
@@ -287,7 +292,8 @@ export class TestStateService {
     });
   }
 
-  private gradingOptions$(gradingScaleId: number) {
+  private gradingOptions$(gradingScaleId: number | null) {
+    if (gradingScaleId === null) return of(null);
     return this.gradingScalesOptions$.pipe(
       map((gradingScaleOptions) => gradingScaleOptions[gradingScaleId]),
       shareReplay(1)
@@ -300,6 +306,7 @@ export class TestStateService {
   ): Observable<number | null> {
     return this.course$.pipe(
       map((course: Course) => {
+        if (course.GradingScaleId === null) return null;
         if (gradingScaleOptions[course.GradingScaleId] === undefined)
           return null;
         const scale = gradingScaleOptions[course.GradingScaleId]!;
diff --git a/src/app/shared/models/course.model.ts b/src/app/shared/models/course.model.ts
index 1cf53726a..6361c651c 100644
--- a/src/app/shared/models/course.model.ts
+++ b/src/app/shared/models/course.model.ts
@@ -103,7 +103,7 @@ const Course = t.type({
   // EventManagers: null,
   // MainEventManagers: null,
   // TimetableEntries: null,
-  GradingScaleId: t.number,
+  GradingScaleId: Option(t.number),
   FinalGrades: Option(t.array(FinalGrading)),
   Gradings: Option(t.array(Grading)),
   Tests: Option(t.array(Test)),
diff --git a/src/app/shared/services/grading-scales-rest.service.ts b/src/app/shared/services/grading-scales-rest.service.ts
index 6007fc420..f962aa6fd 100644
--- a/src/app/shared/services/grading-scales-rest.service.ts
+++ b/src/app/shared/services/grading-scales-rest.service.ts
@@ -1,6 +1,6 @@
 import { HttpClient } from '@angular/common/http';
 import { Inject, Injectable } from '@angular/core';
-import { forkJoin, Observable, shareReplay, switchMap } from 'rxjs';
+import { forkJoin, Observable, of, shareReplay, switchMap } from 'rxjs';
 import { Settings, SETTINGS } from 'src/app/settings';
 import { GradingScale } from '../models/grading-scale.model';
 import { decode } from '../utils/decode';
@@ -14,18 +14,19 @@ export class GradingScalesRestService extends RestService<typeof GradingScale> {
     super(http, settings, GradingScale, 'GradingScales');
   }
 
-  getGradingScale(id: number): Observable<GradingScale> {
+  getGradingScale(id: number | null): Observable<GradingScale | null> {
+    if (id === null) return of(null);
     return this.http
       .get<unknown>(`${this.baseUrl}/${id}`)
       .pipe(switchMap(decode(GradingScale)));
   }
 
   loadGradingScales(
-    observable: Observable<number[]>
-  ): Observable<ReadonlyArray<GradingScale>> {
+    observable: Observable<(number | null)[]>
+  ): Observable<ReadonlyArray<GradingScale | null>> {
     return observable.pipe(
       switchMap((ids) =>
-        forkJoin(ids.map((id: number) => this.getGradingScale(id)))
+        forkJoin(ids.map((id: number | null) => this.getGradingScale(id)))
       ),
       shareReplay(1)
     );