diff --git a/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/NationalIdentityNumber.tsx b/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/NationalIdentityNumber.tsx
index d8117fe13d4..68ba3d1fa13 100644
--- a/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/NationalIdentityNumber.tsx
+++ b/packages/dnb-eufemia/src/extensions/forms/Field/NationalIdentityNumber/NationalIdentityNumber.tsx
@@ -116,6 +116,8 @@ function NationalIdentityNumber(props: Props) {
 }
 
 function is18YearsOrOlder(value: string) {
+  if (value === undefined) return false
+
   function getAge(birthDate: Date): number {
     const today = new Date()
     const age = today.getFullYear() - birthDate.getFullYear()