diff --git a/src/Exception/UniqueTokenIdentifierConstraintViolationException.php b/src/Exception/UniqueTokenIdentifierConstraintViolationException.php
new file mode 100644
index 00000000..816c249f
--- /dev/null
+++ b/src/Exception/UniqueTokenIdentifierConstraintViolationException.php
@@ -0,0 +1,21 @@
+<?php
+/**
+ * @author      Ivan Kurnosov <zerkms@zerkms.com>
+ * @copyright   Copyright (c) Alex Bilbie
+ * @license     http://mit-license.org/
+ *
+ * @link        https://github.com/thephpleague/oauth2-server
+ */
+
+namespace League\OAuth2\Server\Exception;
+
+
+class UniqueTokenIdentifierConstraintViolationException extends OAuthServerException
+{
+    public static function create()
+    {
+        $errorMessage = 'Could not create unique access token identifier';
+
+        return new static($errorMessage, 100, 'access_token_duplicate', 500);
+    }
+}
diff --git a/src/Grant/AbstractGrant.php b/src/Grant/AbstractGrant.php
index 547ab213..38336b76 100644
--- a/src/Grant/AbstractGrant.php
+++ b/src/Grant/AbstractGrant.php
@@ -16,6 +16,7 @@ use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\ClientEntityInterface;
 use League\OAuth2\Server\Entities\ScopeEntityInterface;
 use League\OAuth2\Server\Exception\OAuthServerException;
+use League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException;
 use League\OAuth2\Server\Repositories\AccessTokenRepositoryInterface;
 use League\OAuth2\Server\Repositories\AuthCodeRepositoryInterface;
 use League\OAuth2\Server\Repositories\ClientRepositoryInterface;
@@ -35,6 +36,8 @@ abstract class AbstractGrant implements GrantTypeInterface
 
     const SCOPE_DELIMITER_STRING = ' ';
 
+    const MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS = 10;
+
     /**
      * @var ClientRepositoryInterface
      */
@@ -321,19 +324,28 @@ abstract class AbstractGrant implements GrantTypeInterface
         $userIdentifier,
         array $scopes = []
     ) {
+        $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
+
         $accessToken = $this->accessTokenRepository->getNewToken($client, $scopes, $userIdentifier);
         $accessToken->setClient($client);
         $accessToken->setUserIdentifier($userIdentifier);
-        $accessToken->setIdentifier($this->generateUniqueIdentifier());
         $accessToken->setExpiryDateTime((new \DateTime())->add($accessTokenTTL));
 
         foreach ($scopes as $scope) {
             $accessToken->addScope($scope);
         }
 
-        $this->accessTokenRepository->persistNewAccessToken($accessToken);
-
-        return $accessToken;
+        while ($maxGenerationAttempts-- > 0) {
+            $accessToken->setIdentifier($this->generateUniqueIdentifier());
+            try {
+                $this->accessTokenRepository->persistNewAccessToken($accessToken);
+                return $accessToken;
+            } catch (UniqueTokenIdentifierConstraintViolationException $e) {
+                if ($maxGenerationAttempts === 0) {
+                    throw $e;
+                }
+            }
+        }
     }
 
     /**
@@ -354,8 +366,9 @@ abstract class AbstractGrant implements GrantTypeInterface
         $redirectUri,
         array $scopes = []
     ) {
+        $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
+
         $authCode = $this->authCodeRepository->getNewAuthCode();
-        $authCode->setIdentifier($this->generateUniqueIdentifier());
         $authCode->setExpiryDateTime((new \DateTime())->add($authCodeTTL));
         $authCode->setClient($client);
         $authCode->setUserIdentifier($userIdentifier);
@@ -365,9 +378,17 @@ abstract class AbstractGrant implements GrantTypeInterface
             $authCode->addScope($scope);
         }
 
-        $this->authCodeRepository->persistNewAuthCode($authCode);
-
-        return $authCode;
+        while ($maxGenerationAttempts-- > 0) {
+            $authCode->setIdentifier($this->generateUniqueIdentifier());
+            try {
+                $this->authCodeRepository->persistNewAuthCode($authCode);
+                return $authCode;
+            } catch (UniqueTokenIdentifierConstraintViolationException $e) {
+                if ($maxGenerationAttempts === 0) {
+                    throw $e;
+                }
+            }
+        }
     }
 
     /**
@@ -377,14 +398,23 @@ abstract class AbstractGrant implements GrantTypeInterface
      */
     protected function issueRefreshToken(AccessTokenEntityInterface $accessToken)
     {
+        $maxGenerationAttempts = self::MAX_RANDOM_TOKEN_GENERATION_ATTEMPTS;
+
         $refreshToken = $this->refreshTokenRepository->getNewRefreshToken();
-        $refreshToken->setIdentifier($this->generateUniqueIdentifier());
         $refreshToken->setExpiryDateTime((new \DateTime())->add($this->refreshTokenTTL));
         $refreshToken->setAccessToken($accessToken);
 
-        $this->refreshTokenRepository->persistNewRefreshToken($refreshToken);
-
-        return $refreshToken;
+        while ($maxGenerationAttempts-- > 0) {
+            $refreshToken->setIdentifier($this->generateUniqueIdentifier());
+            try {
+                $this->refreshTokenRepository->persistNewRefreshToken($refreshToken);
+                return $refreshToken;
+            } catch (UniqueTokenIdentifierConstraintViolationException $e) {
+                if ($maxGenerationAttempts === 0) {
+                    throw $e;
+                }
+            }
+        }
     }
 
     /**
diff --git a/tests/Grant/AuthCodeGrantTest.php b/tests/Grant/AuthCodeGrantTest.php
index 09ea03e6..8537a1af 100644
--- a/tests/Grant/AuthCodeGrantTest.php
+++ b/tests/Grant/AuthCodeGrantTest.php
@@ -6,6 +6,7 @@ use League\OAuth2\Server\CryptKey;
 use League\OAuth2\Server\Entities\AccessTokenEntityInterface;
 use League\OAuth2\Server\Entities\RefreshTokenEntityInterface;
 use League\OAuth2\Server\Exception\OAuthServerException;
+use League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException;
 use League\OAuth2\Server\Grant\AuthCodeGrant;
 use League\OAuth2\Server\Repositories\AccessTokenRepositoryInterface;
 use League\OAuth2\Server\Repositories\AuthCodeRepositoryInterface;
@@ -1183,4 +1184,299 @@ class AuthCodeGrantTest extends \PHPUnit_Framework_TestCase
             $this->assertEquals($e->getHint(), 'Check the `code_verifier` parameter');
         }
     }
-}
\ No newline at end of file
+
+    public function testAuthCodeRepositoryUniqueConstraintCheck()
+    {
+        $authRequest = new AuthorizationRequest();
+        $authRequest->setAuthorizationApproved(true);
+        $authRequest->setClient(new ClientEntity());
+        $authRequest->setGrantTypeId('authorization_code');
+        $authRequest->setUser(new UserEntity());
+
+        $authCodeRepository = $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock();
+        $authCodeRepository->method('getNewAuthCode')->willReturn(new AuthCodeEntity());
+
+        $authCodeRepository->expects($this->at(0))->method('persistNewAuthCode')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
+        $authCodeRepository->expects($this->at(1))->method('persistNewAuthCode');
+
+        $grant = new AuthCodeGrant(
+            $authCodeRepository,
+            $this->getMock(RefreshTokenRepositoryInterface::class),
+            new \DateInterval('PT10M')
+        );
+
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+
+        $this->assertTrue($grant->completeAuthorizationRequest($authRequest) instanceof RedirectResponse);
+    }
+
+    /**
+     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
+     * @expectedExceptionCode 7
+     */
+    public function testAuthCodeRepositoryFailToPersist()
+    {
+        $authRequest = new AuthorizationRequest();
+        $authRequest->setAuthorizationApproved(true);
+        $authRequest->setClient(new ClientEntity());
+        $authRequest->setGrantTypeId('authorization_code');
+        $authRequest->setUser(new UserEntity());
+
+        $authCodeRepository = $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock();
+        $authCodeRepository->method('getNewAuthCode')->willReturn(new AuthCodeEntity());
+        $authCodeRepository->method('persistNewAuthCode')->willThrowException(OAuthServerException::serverError('something bad happened'));
+
+        $grant = new AuthCodeGrant(
+            $authCodeRepository,
+            $this->getMock(RefreshTokenRepositoryInterface::class),
+            new \DateInterval('PT10M')
+        );
+
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+
+        $this->assertTrue($grant->completeAuthorizationRequest($authRequest) instanceof RedirectResponse);
+    }
+
+    /**
+     * @expectedException \League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException
+     * @expectedExceptionCode 100
+     */
+    public function testAuthCodeRepositoryFailToPersistUniqueNoInfiniteLoop()
+    {
+        $authRequest = new AuthorizationRequest();
+        $authRequest->setAuthorizationApproved(true);
+        $authRequest->setClient(new ClientEntity());
+        $authRequest->setGrantTypeId('authorization_code');
+        $authRequest->setUser(new UserEntity());
+
+        $authCodeRepository = $this->getMockBuilder(AuthCodeRepositoryInterface::class)->getMock();
+        $authCodeRepository->method('getNewAuthCode')->willReturn(new AuthCodeEntity());
+        $authCodeRepository->method('persistNewAuthCode')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
+
+        $grant = new AuthCodeGrant(
+            $authCodeRepository,
+            $this->getMock(RefreshTokenRepositoryInterface::class),
+            new \DateInterval('PT10M')
+        );
+
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+
+        $this->assertTrue($grant->completeAuthorizationRequest($authRequest) instanceof RedirectResponse);
+    }
+
+    public function testRefreshTokenRepositoryUniqueConstraintCheck()
+    {
+        $client = new ClientEntity();
+        $client->setIdentifier('foo');
+        $client->setRedirectUri('http://foo/bar');
+        $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
+        $clientRepositoryMock->method('getClientEntity')->willReturn($client);
+
+        $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
+        $scopeEntity = new ScopeEntity();
+        $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
+        $scopeRepositoryMock->method('finalizeScopes')->willReturnArgument(0);
+
+        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();
+
+        $refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
+        $refreshTokenRepositoryMock->method('getNewRefreshToken')->willReturn(new RefreshTokenEntity());
+        $refreshTokenRepositoryMock->expects($this->at(0))->method('persistNewRefreshToken')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
+        $refreshTokenRepositoryMock->expects($this->at(1))->method('persistNewRefreshToken');
+
+        $grant = new AuthCodeGrant(
+            $this->getMock(AuthCodeRepositoryInterface::class),
+            $this->getMock(RefreshTokenRepositoryInterface::class),
+            new \DateInterval('PT10M')
+        );
+        $grant->setClientRepository($clientRepositoryMock);
+        $grant->setScopeRepository($scopeRepositoryMock);
+        $grant->setAccessTokenRepository($accessTokenRepositoryMock);
+        $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+
+        $request = new ServerRequest(
+            [],
+            [],
+            null,
+            'POST',
+            'php://input',
+            [],
+            [],
+            [],
+            [
+                'grant_type'   => 'authorization_code',
+                'client_id'    => 'foo',
+                'redirect_uri' => 'http://foo/bar',
+                'code'         => $this->cryptStub->doEncrypt(
+                    json_encode(
+                        [
+                            'auth_code_id' => uniqid(),
+                            'expire_time'  => time() + 3600,
+                            'client_id'    => 'foo',
+                            'user_id'      => 123,
+                            'scopes'       => ['foo'],
+                            'redirect_uri' => 'http://foo/bar',
+                        ]
+                    )
+                ),
+            ]
+        );
+
+        /** @var StubResponseType $response */
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+
+        $this->assertTrue($response->getAccessToken() instanceof AccessTokenEntityInterface);
+        $this->assertTrue($response->getRefreshToken() instanceof RefreshTokenEntityInterface);
+    }
+
+    /**
+     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
+     * @expectedExceptionCode 7
+     */
+    public function testRefreshTokenRepositoryFailToPersist()
+    {
+        $client = new ClientEntity();
+        $client->setIdentifier('foo');
+        $client->setRedirectUri('http://foo/bar');
+        $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
+        $clientRepositoryMock->method('getClientEntity')->willReturn($client);
+
+        $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
+        $scopeEntity = new ScopeEntity();
+        $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
+        $scopeRepositoryMock->method('finalizeScopes')->willReturnArgument(0);
+
+        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();
+
+        $refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
+        $refreshTokenRepositoryMock->method('getNewRefreshToken')->willReturn(new RefreshTokenEntity());
+        $refreshTokenRepositoryMock->method('persistNewRefreshToken')->willThrowException(OAuthServerException::serverError('something bad happened'));
+
+        $grant = new AuthCodeGrant(
+            $this->getMock(AuthCodeRepositoryInterface::class),
+            $this->getMock(RefreshTokenRepositoryInterface::class),
+            new \DateInterval('PT10M')
+        );
+        $grant->setClientRepository($clientRepositoryMock);
+        $grant->setScopeRepository($scopeRepositoryMock);
+        $grant->setAccessTokenRepository($accessTokenRepositoryMock);
+        $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+
+        $request = new ServerRequest(
+            [],
+            [],
+            null,
+            'POST',
+            'php://input',
+            [],
+            [],
+            [],
+            [
+                'grant_type'   => 'authorization_code',
+                'client_id'    => 'foo',
+                'redirect_uri' => 'http://foo/bar',
+                'code'         => $this->cryptStub->doEncrypt(
+                    json_encode(
+                        [
+                            'auth_code_id' => uniqid(),
+                            'expire_time'  => time() + 3600,
+                            'client_id'    => 'foo',
+                            'user_id'      => 123,
+                            'scopes'       => ['foo'],
+                            'redirect_uri' => 'http://foo/bar',
+                        ]
+                    )
+                ),
+            ]
+        );
+
+        /** @var StubResponseType $response */
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+
+        $this->assertTrue($response->getAccessToken() instanceof AccessTokenEntityInterface);
+        $this->assertTrue($response->getRefreshToken() instanceof RefreshTokenEntityInterface);
+    }
+
+    /**
+     * @expectedException \League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException
+     * @expectedExceptionCode 100
+     */
+    public function testRefreshTokenRepositoryFailToPersistUniqueNoInfiniteLoop()
+    {
+        $client = new ClientEntity();
+        $client->setIdentifier('foo');
+        $client->setRedirectUri('http://foo/bar');
+        $clientRepositoryMock = $this->getMockBuilder(ClientRepositoryInterface::class)->getMock();
+        $clientRepositoryMock->method('getClientEntity')->willReturn($client);
+
+        $scopeRepositoryMock = $this->getMockBuilder(ScopeRepositoryInterface::class)->getMock();
+        $scopeEntity = new ScopeEntity();
+        $scopeRepositoryMock->method('getScopeEntityByIdentifier')->willReturn($scopeEntity);
+        $scopeRepositoryMock->method('finalizeScopes')->willReturnArgument(0);
+
+        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->method('persistNewAccessToken')->willReturnSelf();
+
+        $refreshTokenRepositoryMock = $this->getMockBuilder(RefreshTokenRepositoryInterface::class)->getMock();
+        $refreshTokenRepositoryMock->method('getNewRefreshToken')->willReturn(new RefreshTokenEntity());
+        $refreshTokenRepositoryMock->method('persistNewRefreshToken')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
+
+        $grant = new AuthCodeGrant(
+            $this->getMock(AuthCodeRepositoryInterface::class),
+            $this->getMock(RefreshTokenRepositoryInterface::class),
+            new \DateInterval('PT10M')
+        );
+        $grant->setClientRepository($clientRepositoryMock);
+        $grant->setScopeRepository($scopeRepositoryMock);
+        $grant->setAccessTokenRepository($accessTokenRepositoryMock);
+        $grant->setRefreshTokenRepository($refreshTokenRepositoryMock);
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+
+        $request = new ServerRequest(
+            [],
+            [],
+            null,
+            'POST',
+            'php://input',
+            [],
+            [],
+            [],
+            [
+                'grant_type'   => 'authorization_code',
+                'client_id'    => 'foo',
+                'redirect_uri' => 'http://foo/bar',
+                'code'         => $this->cryptStub->doEncrypt(
+                    json_encode(
+                        [
+                            'auth_code_id' => uniqid(),
+                            'expire_time'  => time() + 3600,
+                            'client_id'    => 'foo',
+                            'user_id'      => 123,
+                            'scopes'       => ['foo'],
+                            'redirect_uri' => 'http://foo/bar',
+                        ]
+                    )
+                ),
+            ]
+        );
+
+        /** @var StubResponseType $response */
+        $response = $grant->respondToAccessTokenRequest($request, new StubResponseType(), new \DateInterval('PT10M'));
+
+        $this->assertTrue($response->getAccessToken() instanceof AccessTokenEntityInterface);
+        $this->assertTrue($response->getRefreshToken() instanceof RefreshTokenEntityInterface);
+    }
+}
diff --git a/tests/Grant/ImplicitGrantTest.php b/tests/Grant/ImplicitGrantTest.php
index fbf60b8c..0600d4c6 100644
--- a/tests/Grant/ImplicitGrantTest.php
+++ b/tests/Grant/ImplicitGrantTest.php
@@ -3,6 +3,8 @@
 namespace LeagueTests\Grant;
 
 use League\OAuth2\Server\CryptKey;
+use League\OAuth2\Server\Exception\OAuthServerException;
+use League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException;
 use League\OAuth2\Server\Grant\ImplicitGrant;
 use League\OAuth2\Server\Repositories\AccessTokenRepositoryInterface;
 use League\OAuth2\Server\Repositories\ClientRepositoryInterface;
@@ -295,4 +297,76 @@ class ImplicitGrantTest extends \PHPUnit_Framework_TestCase
 
         $grant->completeAuthorizationRequest($authRequest);
     }
+
+    public function testAccessTokenRepositoryUniqueConstraintCheck()
+    {
+        $authRequest = new AuthorizationRequest();
+        $authRequest->setAuthorizationApproved(true);
+        $authRequest->setClient(new ClientEntity());
+        $authRequest->setGrantTypeId('authorization_code');
+        $authRequest->setUser(new UserEntity());
+
+        /** @var AccessTokenRepositoryInterface|\PHPUnit_Framework_MockObject_MockObject $accessTokenRepositoryMock */
+        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->expects($this->at(0))->method('persistNewAccessToken')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
+        $accessTokenRepositoryMock->expects($this->at(1))->method('persistNewAccessToken')->willReturnSelf();
+
+        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+        $grant->setAccessTokenRepository($accessTokenRepositoryMock);
+
+        $this->assertTrue($grant->completeAuthorizationRequest($authRequest) instanceof RedirectResponse);
+    }
+
+    /**
+     * @expectedException \League\OAuth2\Server\Exception\OAuthServerException
+     * @expectedExceptionCode 7
+     */
+    public function testAccessTokenRepositoryFailToPersist()
+    {
+        $authRequest = new AuthorizationRequest();
+        $authRequest->setAuthorizationApproved(true);
+        $authRequest->setClient(new ClientEntity());
+        $authRequest->setGrantTypeId('authorization_code');
+        $authRequest->setUser(new UserEntity());
+
+        /** @var AccessTokenRepositoryInterface|\PHPUnit_Framework_MockObject_MockObject $accessTokenRepositoryMock */
+        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->method('persistNewAccessToken')->willThrowException(OAuthServerException::serverError('something bad happened'));
+
+        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+        $grant->setAccessTokenRepository($accessTokenRepositoryMock);
+
+        $grant->completeAuthorizationRequest($authRequest);
+    }
+
+    /**
+     * @expectedException \League\OAuth2\Server\Exception\UniqueTokenIdentifierConstraintViolationException
+     * @expectedExceptionCode 100
+     */
+    public function testAccessTokenRepositoryFailToPersistUniqueNoInfiniteLoop()
+    {
+        $authRequest = new AuthorizationRequest();
+        $authRequest->setAuthorizationApproved(true);
+        $authRequest->setClient(new ClientEntity());
+        $authRequest->setGrantTypeId('authorization_code');
+        $authRequest->setUser(new UserEntity());
+
+        /** @var AccessTokenRepositoryInterface|\PHPUnit_Framework_MockObject_MockObject $accessTokenRepositoryMock */
+        $accessTokenRepositoryMock = $this->getMockBuilder(AccessTokenRepositoryInterface::class)->getMock();
+        $accessTokenRepositoryMock->method('getNewToken')->willReturn(new AccessTokenEntity());
+        $accessTokenRepositoryMock->method('persistNewAccessToken')->willThrowException(UniqueTokenIdentifierConstraintViolationException::create());
+
+        $grant = new ImplicitGrant(new \DateInterval('PT10M'));
+        $grant->setPrivateKey(new CryptKey('file://' . __DIR__ . '/../Stubs/private.key'));
+        $grant->setPublicKey(new CryptKey('file://' . __DIR__ . '/../Stubs/public.key'));
+        $grant->setAccessTokenRepository($accessTokenRepositoryMock);
+
+        $grant->completeAuthorizationRequest($authRequest);
+    }
 }