diff --git a/CHANGELOG.md b/CHANGELOG.md
index d853df2..b22d1ab 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 - Dropped support for PHP 7.4 and PHP 8.0
 
+### Deprecated
+
+- `\Art4\Accessable::get()` will add `mixed` as a native return type declaration in 2.0.0, do the same in your implementation now to avoid errors.
+- `\Art4\Manager::getParam()` will add `mixed` as a native return type declaration in 2.0.0, do the same in your implementation now to avoid errors.
+
 ## [1.2.0 - 2023-11-28](https://github.com/Art4/json-api-client/compare/1.1.0...1.2.0)
 
 ### Added
diff --git a/src/Accessable.php b/src/Accessable.php
index 11f3c93..90798ce 100644
--- a/src/Accessable.php
+++ b/src/Accessable.php
@@ -18,22 +18,20 @@ interface Accessable
     /**
      * Get a value by a key
      *
-     * @param mixed $key The key
+     * @return-type-will-change mixed `\Art4\JsonApiClient\Accessable::get()` will add `mixed` as a native return type declaration in 2.0.0, do the same in your implementation now to avoid errors.
      *
      * @return mixed
      */
-    public function get($key);
+    public function get(mixed $key)/*: mixed */;
 
     /**
      * Check if a value exists
      *
      * @return-type-will-change bool `\Art4\JsonApiClient\Accessable::has()` will add `bool` as a native return type declaration in 2.0.0, do the same in your implementation now to avoid errors.
      *
-     * @param mixed $key The key
-     *
      * @return bool
      */
-    public function has($key)/*: bool */;
+    public function has(mixed $key)/*: bool */;
 
     /**
      * Returns the keys of all setted values
diff --git a/src/Element.php b/src/Element.php
index 2951a2e..0bc71ba 100644
--- a/src/Element.php
+++ b/src/Element.php
@@ -18,5 +18,5 @@ interface Element
      *
      * @param mixed $data The data for this Element
      */
-    public function __construct($data, Manager $manager, Accessable $parent);
+    public function __construct(mixed $data, Manager $manager, Accessable $parent);
 }
diff --git a/src/Helper/AbstractElement.php b/src/Helper/AbstractElement.php
index f15a62c..016b25e 100644
--- a/src/Helper/AbstractElement.php
+++ b/src/Helper/AbstractElement.php
@@ -30,7 +30,7 @@ abstract class AbstractElement implements Accessable, Element
      *
      * @param mixed $data The data for this Element
      */
-    public function __construct($data, Manager $manager, Accessable $parent)
+    public function __construct(mixed $data, Manager $manager, Accessable $parent)
     {
         $this->manager = $manager;
         $this->parent = $parent;
@@ -56,10 +56,8 @@ protected function getParent(): Accessable
 
     /**
      * Create an element
-     *
-     * @param mixed $data
      */
-    protected function create(string $name, $data): Accessable
+    protected function create(string $name, mixed $data): Accessable
     {
         return $this->getManager()->getFactory()->make(
             $name,
@@ -69,8 +67,6 @@ protected function create(string $name, $data): Accessable
 
     /**
      * Parse the data
-     *
-     * @param mixed $data
      */
-    abstract protected function parse($data): void;
+    abstract protected function parse(mixed $data): void;
 }
diff --git a/src/Manager.php b/src/Manager.php
index 0610da0..4f38c72 100644
--- a/src/Manager.php
+++ b/src/Manager.php
@@ -39,9 +39,9 @@ public function getFactory()/*: Factory */;
     /**
      * Get a param by key
      *
-     * @param mixed $default
+     * @return-type-will-change mixed `\Art4\JsonApiClient\Manager::getParam()` will add `mixed` as a native return type declaration in 2.0.0, do the same in your implementation now to avoid errors.
      *
      * @return mixed
      */
-    public function getParam(string $key, $default);
+    public function getParam(string $key, mixed $default)/*: mixed*/;
 }
diff --git a/tests/Unit/Helper/AccessableTraitTest.php b/tests/Unit/Helper/AccessableTraitTest.php
index f52ef81..583f436 100644
--- a/tests/Unit/Helper/AccessableTraitTest.php
+++ b/tests/Unit/Helper/AccessableTraitTest.php
@@ -19,10 +19,8 @@ class AccessableTraitTest extends TestCase
 
     /**
      * @dataProvider jsonValuesProviderWithoutStringAndInt
-     *
-     * @param mixed $key
      */
-    public function testHasWithInvalidKeyTypeTriggersDeprecationError($key): void
+    public function testHasWithInvalidKeyTypeTriggersDeprecationError(mixed $key): void
     {
         $resource = new AccessableTraitMock();
 
@@ -45,10 +43,8 @@ function ($errno, $errstr) use ($key): bool {
 
     /**
      * @dataProvider jsonValuesProviderWithoutStringAndInt
-     *
-     * @param mixed $key
      */
-    public function testGetWithInvalidKeyTypeTriggersDeprecationError($key): void
+    public function testGetWithInvalidKeyTypeTriggersDeprecationError(mixed $key): void
     {
         $resource = new AccessableTraitMock();