diff --git a/src/CryptKey.php b/src/CryptKey.php
index 0d7a0355..0b6343d9 100644
--- a/src/CryptKey.php
+++ b/src/CryptKey.php
@@ -101,12 +101,12 @@ class CryptKey implements CryptKeyInterface
         return 'file://' . $keyPath;
     }
 
-    public function getKeyPath(): string
+    public function getKeyPath()
     {
         return $this->keyPath;
     }
 
-    public function getPassPhrase(): ?string
+    public function getPassPhrase()
     {
         return $this->passPhrase;
     }
diff --git a/src/CryptKeyInterface.php b/src/CryptKeyInterface.php
index 115f21b2..86c7b044 100644
--- a/src/CryptKeyInterface.php
+++ b/src/CryptKeyInterface.php
@@ -1,5 +1,4 @@
 <?php
-declare(strict_types=1);
 
 namespace League\OAuth2\Server;
 
@@ -10,12 +9,12 @@ interface CryptKeyInterface
      *
      * @return string
      */
-    public function getKeyPath(): string;
+    public function getKeyPath();
 
     /**
      * Retrieve key pass phrase.
      *
      * @return null|string
      */
-    public function getPassPhrase(): ?string;
+    public function getPassPhrase();
 }
diff --git a/tests/AuthorizationServerTest.php b/tests/AuthorizationServerTest.php
index 76bcdda8..72d360a1 100644
--- a/tests/AuthorizationServerTest.php
+++ b/tests/AuthorizationServerTest.php
@@ -4,6 +4,7 @@ namespace LeagueTests;
 
 use DateInterval;
 use League\OAuth2\Server\AuthorizationServer;
+use League\OAuth2\Server\CryptKeyInterface;
 use League\OAuth2\Server\Exception\OAuthServerException;
 use League\OAuth2\Server\Grant\AuthCodeGrant;
 use League\OAuth2\Server\Grant\ClientCredentialsGrant;
@@ -152,7 +153,7 @@ class AuthorizationServerTest extends TestCase
         $encryptionKey = 'file://' . __DIR__ . '/Stubs/public.key';
 
         $responseTypePrototype = new class extends BearerTokenResponse {
-            /* @return null|\League\OAuth2\Server\CryptKeyInterface */
+            /* @return null|CryptKeyInterface */
             public function getPrivateKey()
             {
                 return $this->privateKey;