diff --git a/CHANGELOG.md b/CHANGELOG.md
index d76cf465996..6fdeacda906 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Release Notes for Craft CMS 5
 
+## Unreleased
+
+- Fixed a bug where passkeys created before updating to Craft 5.10 could no longer be used to log in. ([#19530](https://github.com/craftcms/cms/issues/19530), [#19536](https://github.com/craftcms/cms/pull/19536))
+
 ## 5.11.0 - 2026-09-01
 
 > [!WARNING]  
diff --git a/src/auth/passkeys/CredentialRepository.php b/src/auth/passkeys/CredentialRepository.php
index 17251a0b9a5..5313d93c34c 100644
--- a/src/auth/passkeys/CredentialRepository.php
+++ b/src/auth/passkeys/CredentialRepository.php
@@ -8,13 +8,12 @@
 namespace craft\auth\passkeys;
 
 use Craft;
+use craft\elements\User;
 use craft\helpers\DateTimeHelper;
 use craft\helpers\Db;
-use craft\helpers\Json;
 use craft\records\WebAuthn;
 use ParagonIE\ConstantTime\Base64UrlSafe;
 use Webauthn\CredentialRecord;
-use Webauthn\Exception\InvalidDataException;
 use Webauthn\PublicKeyCredentialUserEntity;
 use Webauthn\Util\Base64;
 
@@ -29,7 +28,7 @@ class CredentialRepository
     /**
      * Finds a webauthn record in the database for given id and returns the CredentialRecord for its credential value.
      */
-    public function findOneByCredentialId(string $publicKeyCredentialId, bool $checkOldUserHandle = false): ?CredentialRecord
+    public function findOneByCredentialId(string $publicKeyCredentialId): ?CredentialRecord
     {
         $record = $this->_findByCredentialId($publicKeyCredentialId);
 
@@ -42,19 +41,13 @@ public function findOneByCredentialId(string $publicKeyCredentialId, bool $check
                 'json',
             );
 
-            // if the record was created using webauthn v4 then the credential was run through Json::encode() before storing in the DB,
-            // without the extra base64 encoding pass that webauthn 5's CredentialRecordDenormalizer::normalize() applies;
-            // deserialising such a value therefore leaves the userHandle one decode pass short of where it should be,
-            // so if we failed to log the user in based on the handle mismatch exception, we'll try again, decoding the
-            // stored (old, singly-encoded) handle ourselves to get it to the same (raw) form the assertion response is in
-            if ($checkOldUserHandle) {
-                $credential = Json::decodeIfJson($record->credential);
-                try {
-                    $credentialRecord->userHandle = Base64::decode($credential['userHandle']);
-                } catch (InvalidDataException) {
-                    // not base64-encoded after all; fall back to using it as-is
-                    $credentialRecord->userHandle = $credential['userHandle'];
-                }
+            // if the userHandle is already a fully decoded user UID it means it was created with webauthn v4;
+            // in that case, we should be able to find user by it
+            $found = User::find()->uid($credentialRecord->userHandle)->exists();
+
+            // and if that's the case, we want to base64 encode it again, so that we're comparing correct values
+            if ($found) {
+                $credentialRecord->userHandle = Base64UrlSafe::encodeUnpadded($credentialRecord->userHandle);
             }
 
             return $credentialRecord;
diff --git a/src/elements/User.php b/src/elements/User.php
index e1adb6c424b..b6af7509449 100644
--- a/src/elements/User.php
+++ b/src/elements/User.php
@@ -56,7 +56,6 @@
 use DateInterval;
 use DateTime;
 use DateTimeZone;
-use Webauthn\Exception\InvalidUserHandleException;
 use Webauthn\PublicKeyCredentialRequestOptions;
 use yii\base\Exception;
 use yii\base\InvalidArgumentException;
@@ -1455,26 +1454,15 @@ public function authenticateWithPasskey(
         // Validate the security key
         try {
             $keyValid = $authService->verifyPasskey($this, $requestOptions, $response);
-        } catch (InvalidUserHandleException) {
-            // the user handle may have been stored in the old (pre-webauthn-5) format; try again, accounting for that
-            try {
-                $keyValid = $authService->verifyPasskey($this, $requestOptions, $response, true);
-            } catch (InvalidUserHandleException) {
-                $keyValid = false;
-            }
         } catch (InvalidArgumentException) {
             $keyValid = false;
         }
 
-        $updatedCredentialRecord = Session::remove($authService->passkeyCredSourceParam);
-
         if (!$keyValid) {
             $this->handleInvalidLoginParam();
             return false;
         }
 
-        $authService->webauthnServer()->getCredentialRepository()->saveCredentialSource($updatedCredentialRecord);
-
         $this->authError = $this->_getAuthError();
         return !isset($this->authError);
     }
diff --git a/src/services/Auth.php b/src/services/Auth.php
index 753f610f324..11d13c18f6c 100644
--- a/src/services/Auth.php
+++ b/src/services/Auth.php
@@ -625,7 +625,6 @@ public function verifyPasskey(
 
         $credentialRecord = $this->webauthnServer()->getCredentialRepository()->findOneByCredentialId(
             $publicKeyCredential->rawId,
-            $checkOldUserHandle,
         );
 
         if ($credentialRecord === null) {
@@ -633,24 +632,16 @@ public function verifyPasskey(
             return false;
         }
 
-        // if we're re-checking against the old (pre-webauthn-5) user handle format, $credentialRecord->userHandle
-        // was just set to the decoded (raw) user handle by CredentialRepository::findOneByCredentialId(), so the
-        // user handle we compare it with here needs to be decoded as well, rather than the (encoded) $userEntity->id
-        $userHandle = $checkOldUserHandle ? $user->uid : $userEntity->id;
-
         try {
             $updatedCredentialRecord = $this->webauthnServer()->getAuthenticatorAssertionResponseValidator()->check(
                 $credentialRecord,
                 $authenticatorAssertionResponse,
                 $publicKeyCredentialRequestOptions,
                 Craft::$app->getRequest()->getHostName(),
-                $userHandle,
+                $userEntity->id,
             );
 
-            // we can't save the updated credential record to db here as in User::authenticateWithPasskey()
-            // we might need to call this method (Auth::verifyPasskey()) again, with checkOldUserHandle set to true;
-            // so, we're going to store it in the session and then save from the User::authenticateWithPasskey() method
-            SessionHelper::set($this->passkeyCredSourceParam, $updatedCredentialRecord);
+            $this->webauthnServer()->getCredentialRepository()->saveCredentialSource($updatedCredentialRecord);
         } catch (InvalidUserHandleException $e) {
             throw $e;
         } catch (Throwable $e) {