diff --git a/src/Psl/Collection/IndexAccessInterface.php b/src/Psl/Collection/IndexAccessInterface.php
index 797d23cd..25940b84 100644
--- a/src/Psl/Collection/IndexAccessInterface.php
+++ b/src/Psl/Collection/IndexAccessInterface.php
@@ -34,6 +34,17 @@ public function at(int|string $k): mixed;
      */
     public function contains(int|string $k): bool;
 
+    /**
+     * Alias of `contains`.
+     *
+     * @param Tk $k
+     *
+     * @see contains() method
+     *
+     * @psalm-mutation-free
+     */
+    public function containsKey(int|string $k): bool;
+
     /**
      * Returns the value at the specified key in the current collection.
      *
diff --git a/src/Psl/Collection/Map.php b/src/Psl/Collection/Map.php
index a4abb6ff..3f486fe6 100644
--- a/src/Psl/Collection/Map.php
+++ b/src/Psl/Collection/Map.php
@@ -253,6 +253,18 @@ public function contains(int|string $k): bool
         return array_key_exists($k, $this->elements);
     }
 
+    /**
+     * Alias of `contains`.
+     *
+     * @param Tk $k
+     *
+     * @psalm-mutation-free
+     */
+    public function containsKey(int|string $k): bool
+    {
+        return $this->contains($k);
+    }
+
     /**
      * Returns the value at the specified key in the current map.
      *
diff --git a/src/Psl/Collection/MutableMap.php b/src/Psl/Collection/MutableMap.php
index 12a4d102..7dd1d252 100644
--- a/src/Psl/Collection/MutableMap.php
+++ b/src/Psl/Collection/MutableMap.php
@@ -253,6 +253,18 @@ public function contains(int|string $k): bool
         return array_key_exists($k, $this->elements);
     }
 
+    /**
+     * Alias of `contains`.
+     *
+     * @param Tk $k
+     *
+     * @psalm-mutation-free
+     */
+    public function containsKey(int|string $k): bool
+    {
+        return $this->contains($k);
+    }
+
     /**
      * Returns the value at the specified key in the current map.
      *
diff --git a/src/Psl/Collection/MutableSet.php b/src/Psl/Collection/MutableSet.php
index f58c12bd..21eda1f6 100644
--- a/src/Psl/Collection/MutableSet.php
+++ b/src/Psl/Collection/MutableSet.php
@@ -233,6 +233,20 @@ public function contains(int|string $k): bool
         return array_key_exists($k, $this->elements);
     }
 
+    /**
+     * Alias of `contains`.
+     *
+     * @param T $k
+     *
+     * @return bool True if the value is in the set, false otherwise.
+     *
+     * @psalm-mutation-free
+     */
+    public function containsKey(int|string $k): bool
+    {
+        return $this->contains($k);
+    }
+
     /**
      * Returns the provided value if it is part of the set, or null if it is not.
      *
diff --git a/src/Psl/Collection/MutableVector.php b/src/Psl/Collection/MutableVector.php
index 26c465f0..76915ca0 100644
--- a/src/Psl/Collection/MutableVector.php
+++ b/src/Psl/Collection/MutableVector.php
@@ -204,6 +204,18 @@ public function contains(int|string $k): bool
         return array_key_exists($k, $this->elements);
     }
 
+    /**
+     * Alias of `contains`.
+     *
+     * @param int<0, max> $k
+     *
+     * @psalm-mutation-free
+     */
+    public function containsKey(int|string $k): bool
+    {
+        return $this->contains($k);
+    }
+
     /**
      * Returns the value at the specified key in the current `MutableVector`.
      *
diff --git a/src/Psl/Collection/Set.php b/src/Psl/Collection/Set.php
index 5d91a514..981b4785 100644
--- a/src/Psl/Collection/Set.php
+++ b/src/Psl/Collection/Set.php
@@ -236,6 +236,20 @@ public function contains(int|string $k): bool
         return array_key_exists($k, $this->elements);
     }
 
+    /**
+     * Alias of `contains`.
+     *
+     * @param T $k
+     *
+     * @return bool True if the value is in the set, false otherwise.
+     *
+     * @psalm-mutation-free
+     */
+    public function containsKey(int|string $k): bool
+    {
+        return $this->contains($k);
+    }
+
     /**
      * Returns the provided value if it is part of the set, or null if it is not.
      *
diff --git a/src/Psl/Collection/Vector.php b/src/Psl/Collection/Vector.php
index 964c14c4..1f4e9ba7 100644
--- a/src/Psl/Collection/Vector.php
+++ b/src/Psl/Collection/Vector.php
@@ -204,6 +204,18 @@ public function contains(int|string $k): bool
         return array_key_exists($k, $this->elements);
     }
 
+    /**
+     * Alias of `contains`.
+     *
+     * @param int<0, max> $k
+     *
+     * @psalm-mutation-free
+     */
+    public function containsKey(int|string $k): bool
+    {
+        return $this->contains($k);
+    }
+
     /**
      * Returns the value at the specified key in the current `Vector`.
      *
diff --git a/tests/unit/Collection/MutableMapTest.php b/tests/unit/Collection/MutableMapTest.php
index fce753be..df2ae468 100644
--- a/tests/unit/Collection/MutableMapTest.php
+++ b/tests/unit/Collection/MutableMapTest.php
@@ -235,7 +235,8 @@ public function testOffsetGetThrowsForInvalidOffsetType(): void
         $map[false];
     }
 
-    public function testFromItems(): void {
+    public function testFromItems(): void
+    {
         $map = MutableMap::fromItems([
             'foo' => 'bar',
             'bar' => 'baz',
diff --git a/tests/unit/Collection/SetTest.php b/tests/unit/Collection/SetTest.php
index 2c2bef72..015f5a7c 100644
--- a/tests/unit/Collection/SetTest.php
+++ b/tests/unit/Collection/SetTest.php
@@ -15,7 +15,8 @@ final class SetTest extends AbstractSetTest
      */
     protected string $setClass = Set::class;
 
-    public function testFromItems(): void {
+    public function testFromItems(): void
+    {
         $set = Set::fromItems([
             'foo',
             'bar',