diff --git a/src/enums/MDNodaRepository.php b/src/enums/MDNodaRepository.php
index 290ed6a..b162b33 100644
--- a/src/enums/MDNodaRepository.php
+++ b/src/enums/MDNodaRepository.php
@@ -260,6 +260,15 @@ enum MDNodaRepository implements MDValueEnumInterface, JsonSerializable {
             $id = strtr($id, $toRemove);
         }
 
+        // FILTER_VALIDATE_INT fails on overly large IDs (e.g. VIAF IDs having
+        // more than 20 digits).
+        // In these cases, simply check for the existence of non-numeric characters.
+        if (strlen($id) > 9) {
+            if (empty(trim($id, '0123456789'))) {
+                return $id;
+            }
+        }
+
         // Strings starting with 0 are quite often linked, notably with the NDL.
         // PHP's FILTER_VALIDATE_INT does not accept a leading 0 however, so it
         // is stripped before checking.
@@ -349,15 +358,15 @@ enum MDNodaRepository implements MDValueEnumInterface, JsonSerializable {
             ]);
         }
 
-        if (substr($id, 0, 1) !== 'n') {
-            throw new MDgenericInvalidInputsException("LOC IDs must start with n");
+        if (in_array(substr($id, 0, 2), ['nr', 'nb', 'no'], true)) {
+            if (filter_var(trim(substr($id, 2), '0'), FILTER_VALIDATE_INT) === false) return false;
         }
-
-        if (filter_var(substr($id, 1), FILTER_VALIDATE_INT) === false) {
-            return false;
+        else if (substr($id, 0, 1) === 'n') {
+            if (filter_var(trim(substr($id, 1), '0'), FILTER_VALIDATE_INT) === false) return false;
         }
+        else throw new MDgenericInvalidInputsException("LOC IDs must start with n or nr or nb");
 
-        return $id;
+        return (string)$id;
 
     }
 
@@ -414,6 +423,26 @@ enum MDNodaRepository implements MDValueEnumInterface, JsonSerializable {
 
     }
 
+    /**
+     * Validates a BNF ID. BNF IDs are either fully numeric or end on a single non-numeric character.
+     *
+     * @param string $id ID to validate.
+     *
+     * @return string|false
+     */
+    public static function validateBnfId(string $id):string|false {
+
+        if (!is_numeric(substr($id, -1))) {
+            $validation = self::validateNumericId(substr($id, 0, -1), ["https://catalogue.bnf.fr/ark:/12148/cb"]);
+        }
+        else $validation = self::validateNumericId($id, ["https://catalogue.bnf.fr/ark:/12148/cb"]);
+
+        if ($validation === false) return false;
+
+        return $id;
+
+    }
+
     /**
      * Validates an ID.
      *
@@ -428,7 +457,7 @@ enum MDNodaRepository implements MDValueEnumInterface, JsonSerializable {
             self::aat       => self::validateNumericId($id, ['https://vocab.getty.edu/page/aat/']),
             self::ackerbau  => self::validateNumericId($id, ['https://term.museum-digital.de/ackerbau/tag/']),
             self::bne       => self::validateBneId($id, ['http://datos.bne.es/persona/']),
-            self::bnf       => self::validateNumericId(rtrim($id, 't'), ["https://catalogue.bnf.fr/ark:/12148/cb"]), // cb11960399t is a valid entry, too (general)
+            self::bnf       => self::validateBnfId($id),
             self::cona      => self::validateNumericId($id, ['https://vocab.getty.edu/page/cona/']),
             self::editionhumboldtdigital => self::validateGndId($id, ['https://edition-humboldt.de/register/personen/detail.xql?normid=http://d-nb.info/gnd/']),
             self::gnd       => self::validateGndId($id, ['http://d-nb.info/gnd/', 'https://d-nb.info/gnd/']),
@@ -458,7 +487,10 @@ enum MDNodaRepository implements MDValueEnumInterface, JsonSerializable {
             self::pleiades  => self::validateNumericId($id, ['https://pleiades.stoa.org/places/']),
             self::rkd       => self::validateNumericId($id, ['http://rkd.nl/explore/artists/', 'https://rkd.nl/explore/artists/']),
             self::ulan      => self::validateNumericId($id, ['http://vocab.getty.edu/ulan/', 'http://vocab.getty.edu/page/ulan/', 'https://vocab.getty.edu/page/ulan/']),
-            self::viaf      => self::validateNumericId($id, ['https://viaf.org/viaf/']),
+            self::viaf      => self::validateNumericId($id, [
+                'https://viaf.org/viaf/',
+                'http://viaf.org/viaf/',
+            ]),
             self::wikidata  => self::validateWikidataId($id),
             self::wikipedia => str_replace('https://de.wikipedia.org/wiki/', '', $id),
         };
diff --git a/tests/MDNodaRepositoryTest.php b/tests/MDNodaRepositoryTest.php
index 9c00b14..0ae4c5c 100644
--- a/tests/MDNodaRepositoryTest.php
+++ b/tests/MDNodaRepositoryTest.php
@@ -22,29 +22,34 @@ final class MDNodaRepositoryTest extends TestCase {
     public function testValidIdsValidate():void {
 
         // GND (Germany)
-        self::assertNotFalse(MDNodaRepository::gnd->validateId("https://d-nb.info/gnd/102423008"));
-        self::assertNotFalse(MDNodaRepository::gnd->validateId("http://d-nb.info/gnd/102423008"));
-        self::assertNotFalse(MDNodaRepository::gnd->validateId("102423008"));
+        self::assertEquals("102423008", MDNodaRepository::gnd->validateId("https://d-nb.info/gnd/102423008"));
+        self::assertEquals("102423008", MDNodaRepository::gnd->validateId("http://d-nb.info/gnd/102423008"));
+        self::assertEquals("102423008", MDNodaRepository::gnd->validateId("102423008"));
 
         // NDL (Japan)
-        self::assertNotFalse(MDNodaRepository::ndl->validateId("00967046"));
-        self::assertNotFalse(MDNodaRepository::ndl->validateId("https://id.ndl.go.jp/auth/ndlna/00967046"));
-        self::assertNotFalse(MDNodaRepository::ndl->validateId("http://id.ndl.go.jp/auth/ndlna/00967046"));
+        self::assertEquals("00967046", MDNodaRepository::ndl->validateId("00967046"));
+        self::assertEquals("00967046", MDNodaRepository::ndl->validateId("https://id.ndl.go.jp/auth/ndlna/00967046"));
+        self::assertEquals("00967046", MDNodaRepository::ndl->validateId("http://id.ndl.go.jp/auth/ndlna/00967046"));
 
         // NPG: National Portrait Gallery
-        self::assertNotFalse(MDNodaRepository::npg->validateId("https://www.npg.org.uk/collections/search/person/mp01751"));
+        self::assertEquals('01751', MDNodaRepository::npg->validateId("https://www.npg.org.uk/collections/search/person/mp01751"));
 
         // Library of Congress
-        self::assertNotFalse(MDNodaRepository::loc->validateId("https://id.loc.gov/authorities/names/n2022014604"));
-        self::assertNotFalse(MDNodaRepository::loc->validateId("http://id.loc.gov/authorities/names/n2022014604"));
-        self::assertNotFalse(MDNodaRepository::loc->validateId("n2022014604"));
+        self::assertEquals("n2022014604", MDNodaRepository::loc->validateId("https://id.loc.gov/authorities/names/n2022014604"));
+        self::assertEquals("n2022014604", MDNodaRepository::loc->validateId("http://id.loc.gov/authorities/names/n2022014604"));
+        self::assertEquals("n2022014604", MDNodaRepository::loc->validateId("n2022014604"));
 
-        self::assertNotFalse(MDNodaRepository::lcsh->validateId("https://id.loc.gov/authorities/names/sh2022014604"));
-        self::assertNotFalse(MDNodaRepository::lcsh->validateId("http://id.loc.gov/authorities/names/sh2022014604"));
-        self::assertNotFalse(MDNodaRepository::lcsh->validateId("sh2022014604"));
+        self::assertEquals("sh2022014604", MDNodaRepository::lcsh->validateId("https://id.loc.gov/authorities/names/sh2022014604"));
+        self::assertEquals("sh2022014604", MDNodaRepository::lcsh->validateId("http://id.loc.gov/authorities/names/sh2022014604"));
+        self::assertEquals("sh2022014604", MDNodaRepository::lcsh->validateId("sh2022014604"));
 
-        self::assertNotFalse(MDNodaRepository::bne->validateId("http://datos.bne.es/persona/XX5034943"));
-        self::assertNotFalse(MDNodaRepository::bne->validateId("XX5034943"));
+        self::assertEquals("XX5034943", MDNodaRepository::bne->validateId("http://datos.bne.es/persona/XX5034943"));
+        self::assertEquals("XX5034943", MDNodaRepository::bne->validateId("XX5034943"));
+
+        self::assertEquals("86145857811423020454", MDNodaRepository::viaf->validateId("86145857811423020454"));
+        self::assertEquals("2869150688328112660005", MDNodaRepository::viaf->validateId("2869150688328112660005"));
+        self::assertEquals("248941990", MDNodaRepository::viaf->validateId("https://viaf.org/viaf/248941990"));
+        self::assertEquals("248941990", MDNodaRepository::viaf->validateId("http://viaf.org/viaf/248941990"));
 
     }
 }