diff --git a/alfa-client/libs/tech-shared/src/lib/validation/tech.validation.util.spec.ts b/alfa-client/libs/tech-shared/src/lib/validation/tech.validation.util.spec.ts
index 140ac187955823972d474bcd90c568133b99bde7..dc9b252a76c61cb862874c627c32fd14af236af2 100644
--- a/alfa-client/libs/tech-shared/src/lib/validation/tech.validation.util.spec.ts
+++ b/alfa-client/libs/tech-shared/src/lib/validation/tech.validation.util.spec.ts
@@ -21,23 +21,11 @@
  * Die sprachspezifischen Genehmigungen und Beschränkungen
  * unter der Lizenz sind dem Lizenztext zu entnehmen.
  */
-import {
-  AbstractControl,
-  FormControl,
-  FormGroup,
-  UntypedFormControl,
-  UntypedFormGroup,
-} from '@angular/forms';
-import { createInvalidParam, createIssue } from '../../../test/error';
+import { AbstractControl, FormControl, FormGroup, UntypedFormControl, UntypedFormGroup } from '@angular/forms';
+import { createInvalidParam, createIssue, createProblemDetail } from '../../../test/error';
 import { InvalidParam, Issue } from '../tech.model';
-import {
-  getControlForInvalidParam,
-  getControlForIssue,
-  getFieldPath,
-  getMessageForIssue,
-  setInvalidParamValidationError,
-  setIssueValidationError,
-} from './tech.validation.util';
+import { ValidationMessageCode } from './tech.validation.messages';
+import { getControlForInvalidParam, getControlForIssue, getFieldPath, getMessageForIssue, getMessageReason, setInvalidParamValidationError, setIssueValidationError } from './tech.validation.util';
 
 describe('ValidationUtils', () => {
   const baseField1Control: FormControl = new UntypedFormControl();
@@ -270,4 +258,22 @@ describe('ValidationUtils', () => {
       expect(result).toBe(fieldPath);
     });
   });
+
+  describe('getMessageReason', () => {
+    it('should return reason', () => {
+      const problemDetail = createProblemDetail();
+
+      const reason: ValidationMessageCode = getMessageReason(problemDetail);
+
+      expect(reason).toEqual(problemDetail.invalidParams[0].reason);
+    });
+
+    it('should return null', () => {
+      const problemDetail = createProblemDetail([{ ...createInvalidParam(), reason: null }]);
+
+      const reason: ValidationMessageCode = getMessageReason(problemDetail);
+
+      expect(reason).toBeNull();
+    });
+  });
 });
diff --git a/alfa-client/libs/tech-shared/src/lib/validation/tech.validation.util.ts b/alfa-client/libs/tech-shared/src/lib/validation/tech.validation.util.ts
index 5968495a95e781a0815dd5270f4732d353dea8ee..d562a4543baec28671348cd0ef81402c055b154d 100644
--- a/alfa-client/libs/tech-shared/src/lib/validation/tech.validation.util.ts
+++ b/alfa-client/libs/tech-shared/src/lib/validation/tech.validation.util.ts
@@ -76,7 +76,7 @@ export function isValidationFieldFileSizeExceedError(error: ProblemDetail): bool
   return getMessageReason(error) === ValidationMessageCode.FIELD_FILE_SIZE_EXCEEDED;
 }
 
-export function getMessageReason(problemDetail: ProblemDetail): string {
+export function getMessageReason(problemDetail: ProblemDetail): ValidationMessageCode | null {
   return problemDetail.invalidParams[0].reason ?? null;
 }