diff --git a/src/Metabor/Callback/Composite.php b/src/Metabor/Callback/Composite.php
index 90af8ce..c343ce8 100644
--- a/src/Metabor/Callback/Composite.php
+++ b/src/Metabor/Callback/Composite.php
@@ -27,12 +27,12 @@ public function __invoke(mixed ...$args): mixed
 
     public function attach(CallbackInterface $callback): void
     {
-        $this->callbacks->attach($callback);
+        $this->callbacks->offsetSet($callback, null);
     }
 
     public function detach(CallbackInterface $callback): void
     {
-        $this->callbacks->detach($callback);
+        $this->callbacks->offsetUnset($callback);
     }
 
     public function getIterator(): \Traversable
diff --git a/src/Metabor/Event/Event.php b/src/Metabor/Event/Event.php
index a082744..dcd27d7 100644
--- a/src/Metabor/Event/Event.php
+++ b/src/Metabor/Event/Event.php
@@ -48,12 +48,12 @@ public function getName(): string
 
     public function attach(\SplObserver $observer): void
     {
-        $this->observers->attach($observer);
+        $this->observers->offsetSet($observer, null);
     }
 
     public function detach(\SplObserver $observer): void
     {
-        $this->observers->detach($observer);
+        $this->observers->offsetUnset($observer);
     }
 
     public function notify(): void
diff --git a/src/Metabor/KeyValue/Composite.php b/src/Metabor/KeyValue/Composite.php
index 53680a5..8b58f5c 100644
--- a/src/Metabor/KeyValue/Composite.php
+++ b/src/Metabor/KeyValue/Composite.php
@@ -16,12 +16,12 @@ public function __construct()
 
     public function attach(\ArrayAccess $keyValue): void
     {
-        $this->container->attach($keyValue);
+        $this->container->offsetSet($keyValue, null);
     }
 
     public function detach(\ArrayAccess $keyValue): void
     {
-        $this->container->detach($keyValue);
+        $this->container->offsetUnset($keyValue);
     }
 
     public function offsetExists(mixed $offset): bool
diff --git a/src/Metabor/Observer/Subject.php b/src/Metabor/Observer/Subject.php
index 487a6c9..f7ef902 100644
--- a/src/Metabor/Observer/Subject.php
+++ b/src/Metabor/Observer/Subject.php
@@ -17,12 +17,12 @@ public function __construct()
 
     public function attach(\SplObserver $observer): void
     {
-        $this->observers->attach($observer);
+        $this->observers->offsetSet($observer, null);
     }
 
     public function detach(\SplObserver $observer): void
     {
-        $this->observers->detach($observer);
+        $this->observers->offsetUnset($observer);
     }
 
     public function notify(): void
diff --git a/src/Metabor/Statemachine/Factory/Factory.php b/src/Metabor/Statemachine/Factory/Factory.php
index 731960c..10c4eda 100644
--- a/src/Metabor/Statemachine/Factory/Factory.php
+++ b/src/Metabor/Statemachine/Factory/Factory.php
@@ -41,12 +41,12 @@ public function setTransitonSelector(TransitionSelectorInterface $transitionSele
 
     public function attachStatemachineObserver(\SplObserver $observer): void
     {
-        $this->statemachineObserver->attach($observer);
+        $this->statemachineObserver->offsetSet($observer, null);
     }
 
     public function detachStatemachineObserver(\SplObserver $observer): void
     {
-        $this->statemachineObserver->detach($observer);
+        $this->statemachineObserver->offsetUnset($observer);
     }
 
     public function getStatemachineObserver(): \Traversable
diff --git a/src/Metabor/Statemachine/Graph/GraphBuilder.php b/src/Metabor/Statemachine/Graph/GraphBuilder.php
index e3838a4..c9b05e0 100644
--- a/src/Metabor/Statemachine/Graph/GraphBuilder.php
+++ b/src/Metabor/Statemachine/Graph/GraphBuilder.php
@@ -88,7 +88,7 @@ public function setStateLayout($flag, $value, array $layout)
      */
     public function attachLayoutCallback(Callback $callback)
     {
-        $this->layoutCallback->attach($callback);
+        $this->layoutCallback->offsetSet($callback, null);
     }
 
     /**
@@ -96,7 +96,7 @@ public function attachLayoutCallback(Callback $callback)
      */
     public function detachLayoutCallback(Callback $callback)
     {
-        $this->layoutCallback->detach($callback);
+        $this->layoutCallback->offsetUnset($callback);
     }
 
     /**
diff --git a/src/Metabor/Statemachine/Observer/SubjectHasUpdated.php b/src/Metabor/Statemachine/Observer/SubjectHasUpdated.php
index 64fff59..bf0468c 100644
--- a/src/Metabor/Statemachine/Observer/SubjectHasUpdated.php
+++ b/src/Metabor/Statemachine/Observer/SubjectHasUpdated.php
@@ -12,9 +12,9 @@ class SubjectHasUpdated extends \SplObjectStorage implements \SplObserver
     public function update(\SplSubject $subject): void
     {
         if ($subject instanceof StatemachineInterface) {
-            $this->attach($subject->getSubject());
+            $this->offsetSet($subject->getSubject(), null);
         } else {
-            $this->attach($subject);
+            $this->offsetSet($subject, null);
         }
     }
 }
diff --git a/src/Metabor/Statemachine/State.php b/src/Metabor/Statemachine/State.php
index d6c7164..ac78012 100644
--- a/src/Metabor/Statemachine/State.php
+++ b/src/Metabor/Statemachine/State.php
@@ -36,7 +36,7 @@ public function getTransitions(): \Traversable
 
     public function addTransition(TransitionInterface $transition): void
     {
-        $this->transitions->attach($transition);
+        $this->transitions->offsetSet($transition, null);
         $eventName = $transition->getEventName();
         if ($eventName) {
             $this->getEvent($eventName);
diff --git a/tests/Metabor/KeyValue/FilterTest.php b/tests/Metabor/KeyValue/FilterTest.php
index a4b956c..dc03fb9 100644
--- a/tests/Metabor/KeyValue/FilterTest.php
+++ b/tests/Metabor/KeyValue/FilterTest.php
@@ -19,10 +19,10 @@ public function testFiltersArrayAccessObjectsByCriteria(): void
         $iterator = new \SplObjectStorage();
         $keyValue1 = new \ArrayIterator();
         $keyValue1[$key] = $value1;
-        $iterator->attach($keyValue1);
+        $iterator->offsetSet($keyValue1, null);
         $keyValue2 = new \ArrayIterator();
         $keyValue2[$key] = $value2;
-        $iterator->attach($keyValue2);
+        $iterator->offsetSet($keyValue2, null);
 
         $criteria = new Criteria(array($key => $value1));
         $filtered = new Filter($iterator, $criteria);
diff --git a/tests/Metabor/Statemachine/Transition/ActiveTransitionFilterTest.php b/tests/Metabor/Statemachine/Transition/ActiveTransitionFilterTest.php
index d6f39cc..b5290b5 100644
--- a/tests/Metabor/Statemachine/Transition/ActiveTransitionFilterTest.php
+++ b/tests/Metabor/Statemachine/Transition/ActiveTransitionFilterTest.php
@@ -37,9 +37,9 @@ public function testFiltersAllNotActiveTransitions(): void
 
         $transitions = new \SplObjectStorage();
         $transitionActive = $this->createTransition(true, $subject, $context, $event);
-        $transitions->attach($transitionActive);
+        $transitions->offsetSet($transitionActive, null);
         $transitionNotActive = $this->createTransition(false, $subject, $context, $event);
-        $transitions->attach($transitionNotActive);
+        $transitions->offsetSet($transitionNotActive, null);
 
         $filteredTransitions = new ActiveTransitionFilter($transitions, $subject, $context, $event);
         $this->assertContains($transitionActive, $filteredTransitions);