From 0f4f5c43c8cf322ba75b56ade5c9d0ea2d644f4b Mon Sep 17 00:00:00 2001
From: Yarchik <spoko.dev@gmail.com>
Date: Mon, 22 Jun 2026 20:43:40 +0100
Subject: [PATCH] fix(BY): allow digits in the Belarus bank identifier (4!c)

The Belarus BBAN structure is 4!c4!n16!c per the ISO 13616 / SWIFT IBAN
Registry, so the 4-character bank identifier is alphanumeric (digits or
uppercase letters), not letters only. The regexp encoded it as [A-Z]{4},
which falsely rejects otherwise-valid Belarus IBANs whose bank code
contains a digit, e.g. BY26AKB10100000002966000000A (mod-97 check digits
are valid). The neighbouring branch field [0-9]{4} (4!n) and account
field [A-Z0-9]{16} (16!c) are already correct; only the bank field was
too strict. Change [A-Z]{4} to [A-Z0-9]{4}.
---
 src/ibantools.ts       | 2 +-
 test/ibantools_test.js | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/ibantools.ts b/src/ibantools.ts
index f565bdd..b97c5ce 100755
--- a/src/ibantools.ts
+++ b/src/ibantools.ts
@@ -1038,7 +1038,7 @@ export const countrySpecs: CountryMapInternal = {
   BW: {},
   BY: {
     chars: 28,
-    bban_regexp: '^[A-Z]{4}[0-9]{4}[A-Z0-9]{16}$',
+    bban_regexp: '^[A-Z0-9]{4}[0-9]{4}[A-Z0-9]{16}$',
     IBANRegistry: true,
     bank_identifier: '0-3',
   },
diff --git a/test/ibantools_test.js b/test/ibantools_test.js
index 037a995..de0ab76 100644
--- a/test/ibantools_test.js
+++ b/test/ibantools_test.js
@@ -33,6 +33,9 @@ describe('IBANTools', function() {
     it('with valid BY IBAN should return true', function() {
       return expect(iban.isValidIBAN('BY13NBRB3600900000002Z00AB00')).to.be.true;
     });
+    it('with valid BY IBAN whose bank code contains a digit should return true', function() {
+      return expect(iban.isValidIBAN('BY26AKB10100000002966000000A')).to.be.true;
+    });
     it('with valid CR IBAN should return true', function() {
       return expect(iban.isValidIBAN('CR25010200009074883572')).to.be.true;
     });