diff --git a/CHANGELOG.md b/CHANGELOG.md
index 479deb8..e5312d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Change Log
 
+### Added
+
+- Generic annotations
+
 ## 1.1.0 - 2020-07-07
 
 ### Added
diff --git a/src/FulfilledPromise.php b/src/FulfilledPromise.php
index b0e1574..dce0431 100644
--- a/src/FulfilledPromise.php
+++ b/src/FulfilledPromise.php
@@ -6,14 +6,21 @@
  * A promise already fulfilled.
  *
  * @author Joel Wurtz <joel.wurtz@gmail.com>
+ *
+ * @template-covariant T
+ *
+ * @implements Promise<T>
  */
 final class FulfilledPromise implements Promise
 {
     /**
-     * @var mixed
+     * @var T
      */
     private $result;
 
+    /**
+     * @param T $result
+     */
     public function __construct($result)
     {
         $this->result = $result;
diff --git a/src/Promise.php b/src/Promise.php
index 3258ed0..9383726 100644
--- a/src/Promise.php
+++ b/src/Promise.php
@@ -12,6 +12,8 @@
  *
  * @author Joel Wurtz <joel.wurtz@gmail.com>
  * @author Márk Sági-Kazár <mark.sagikazar@gmail.com>
+ *
+ * @template-covariant T
  */
 interface Promise
 {
@@ -36,10 +38,12 @@ interface Promise
      * If you do not care about one of the cases, you can set the corresponding callable to null
      * The callback will be called when the value arrived and never more than once.
      *
-     * @param callable|null $onFulfilled called when a response will be available
-     * @param callable|null $onRejected  called when an exception occurs
+     * @param callable(T): V|null          $onFulfilled called when a response will be available
+     * @param callable(\Exception): V|null $onRejected  called when an exception occurs
+     *
+     * @return Promise<V> a new resolved promise with value of the executed callback (onFulfilled / onRejected)
      *
-     * @return Promise a new resolved promise with value of the executed callback (onFulfilled / onRejected)
+     * @template V
      */
     public function then(callable $onFulfilled = null, callable $onRejected = null);
 
@@ -61,7 +65,7 @@ public function getState();
      *
      * @param bool $unwrap Whether to return resolved value / throw reason or not
      *
-     * @return mixed Resolved value, null if $unwrap is set to false
+     * @return T Resolved value, null if $unwrap is set to false
      *
      * @throws \Exception the rejection reason if $unwrap is set to true and the request failed
      */
diff --git a/src/RejectedPromise.php b/src/RejectedPromise.php
index 058d0fd..2cbefec 100644
--- a/src/RejectedPromise.php
+++ b/src/RejectedPromise.php
@@ -6,6 +6,10 @@
  * A rejected promise.
  *
  * @author Joel Wurtz <joel.wurtz@gmail.com>
+ *
+ * @template-covariant T
+ *
+ * @implements Promise<T>
  */
 final class RejectedPromise implements Promise
 {