diff --git a/src/Concerns/Extendable.php b/src/Concerns/Extendable.php
index a2f7e40b..1ff6626b 100644
--- a/src/Concerns/Extendable.php
+++ b/src/Concerns/Extendable.php
@@ -8,6 +8,8 @@ use Closure;
 
 /**
  * @internal
+ *
+ * @template T of object
  */
 trait Extendable
 {
@@ -20,6 +22,8 @@ trait Extendable
 
     /**
      * Register a new extend.
+     *
+     * @param-closure-this T $extend
      */
     public function extend(string $name, Closure $extend): void
     {
diff --git a/src/Expectation.php b/src/Expectation.php
index 8091ad82..50729d7a 100644
--- a/src/Expectation.php
+++ b/src/Expectation.php
@@ -52,7 +52,9 @@ use ReflectionProperty;
  */
 final class Expectation
 {
+    /** @use Extendable<self<TValue>> */
     use Extendable;
+
     use Pipeable;
     use Retrievable;