From b06a89d65746e93945b17d55a048d4a96a5e1641 Mon Sep 17 00:00:00 2001
From: Johannes Haukland <42615991+HauklandJ@users.noreply.github.com>
Date: Fri, 7 Nov 2025 10:10:34 +0100
Subject: [PATCH] fix: orgnr validation (#3838)

---
 .../OrganisationLookup/validation.test.ts     | 33 +++++++++++++++++++
 src/layout/OrganisationLookup/validation.ts   |  9 ++++-
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/src/layout/OrganisationLookup/validation.test.ts b/src/layout/OrganisationLookup/validation.test.ts
index 66b50103a9..5781972137 100644
--- a/src/layout/OrganisationLookup/validation.test.ts
+++ b/src/layout/OrganisationLookup/validation.test.ts
@@ -4,6 +4,39 @@ describe('CheckValidOrgNr', () => {
   it('should return true when the orgNr is valid', () => {
     expect(checkValidOrgnNr('043871668')).toBe(true);
   });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('974683520')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('900010605')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('123778847')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('344547211')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('542683430')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('473324261')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('883863631')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('594027922')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('688701473')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('696902453')).toBe(true);
+  });
+  it('should return true when the orgNr is valid', () => {
+    expect(checkValidOrgnNr('899350766')).toBe(true);
+  });
   it('should return false when the orgNr is invalid', () => {
     expect(checkValidOrgnNr('143871668')).toBe(false);
   });
diff --git a/src/layout/OrganisationLookup/validation.ts b/src/layout/OrganisationLookup/validation.ts
index 0f44271860..b04b8cccea 100644
--- a/src/layout/OrganisationLookup/validation.ts
+++ b/src/layout/OrganisationLookup/validation.ts
@@ -42,13 +42,20 @@ export function checkValidOrgnNr(orgNr: string): boolean {
 
   const [w1, w2, w3, w4, w5, w6, w7, w8] = [3, 2, 7, 6, 5, 4, 3, 2];
   const sum = a1 * w1 + a2 * w2 + a3 * w3 + a4 * w4 + a5 * w5 + a6 * w6 + a7 * w7 + a8 * w8;
-  const calculatedCheckDigit = 11 - (sum % 11);
+
+  let calculatedCheckDigit = mod11(sum);
+
+  if (calculatedCheckDigit === 11) {
+    calculatedCheckDigit = 0;
+  }
 
   return calculatedCheckDigit === allegedCheckDigit;
 }
 
 export const validateOrgnr = ajv.compile(orgNrSchema);
 
+const mod11 = (value: number): number => 11 - (value % 11);
+
 const organisationLookupResponseSchema: JSONSchemaType<OrganisationLookupResponse> = {
   type: 'object',
   oneOf: [