diff --git a/src/CompositeCancellation.php b/src/CompositeCancellation.php
index 678a65ea..bdfccdde 100644
--- a/src/CompositeCancellation.php
+++ b/src/CompositeCancellation.php
@@ -6,6 +6,9 @@
 
 final class CompositeCancellation implements Cancellation
 {
+    use ForbidCloning;
+    use ForbidSerialization;
+
     /** @var array<int, array{Cancellation, string}> */
     private array $cancellations = [];
 
diff --git a/src/DeferredCancellation.php b/src/DeferredCancellation.php
index 6915f80a..4d9d56ea 100644
--- a/src/DeferredCancellation.php
+++ b/src/DeferredCancellation.php
@@ -37,6 +37,9 @@
  */
 final class DeferredCancellation
 {
+    use ForbidCloning;
+    use ForbidSerialization;
+
     private readonly Internal\Cancellable $source;
     private readonly Cancellation $cancellation;
 
diff --git a/src/DeferredFuture.php b/src/DeferredFuture.php
index 583653e0..38f8ee6b 100644
--- a/src/DeferredFuture.php
+++ b/src/DeferredFuture.php
@@ -7,6 +7,9 @@
  */
 final class DeferredFuture
 {
+    use ForbidCloning;
+    use ForbidSerialization;
+
     /** @var Internal\FutureState<T> */
     private readonly Internal\FutureState $state;
 
diff --git a/src/ForbidCloning.php b/src/ForbidCloning.php
new file mode 100644
index 00000000..92c588f4
--- /dev/null
+++ b/src/ForbidCloning.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace Amp;
+
+trait ForbidCloning
+{
+    final protected function __clone()
+    {
+        throw new \Error(__CLASS__ . ' does not support cloning');
+    }
+}
diff --git a/src/ForbidSerialization.php b/src/ForbidSerialization.php
new file mode 100644
index 00000000..d8669a1d
--- /dev/null
+++ b/src/ForbidSerialization.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace Amp;
+
+trait ForbidSerialization
+{
+    final public function __serialize(): never
+    {
+        throw new \Error(__CLASS__ . ' does not support serialization');
+    }
+}
diff --git a/src/Future.php b/src/Future.php
index 52b9c032..a563412e 100644
--- a/src/Future.php
+++ b/src/Future.php
@@ -11,6 +11,9 @@
  */
 final class Future
 {
+    use ForbidCloning;
+    use ForbidSerialization;
+
     /**
      * Iterate over the given futures in completion order.
      *
diff --git a/src/Internal/Cancellable.php b/src/Internal/Cancellable.php
index a69bda07..677bda17 100644
--- a/src/Internal/Cancellable.php
+++ b/src/Internal/Cancellable.php
@@ -4,6 +4,8 @@
 
 use Amp\Cancellation;
 use Amp\CancelledException;
+use Amp\ForbidCloning;
+use Amp\ForbidSerialization;
 use Revolt\EventLoop;
 
 /**
@@ -13,6 +15,9 @@
  */
 final class Cancellable implements Cancellation
 {
+    use ForbidCloning;
+    use ForbidSerialization;
+
     private string $nextId = "a";
 
     /** @var \Closure[] */
diff --git a/src/Internal/FutureIterator.php b/src/Internal/FutureIterator.php
index 14996d98..db92099f 100644
--- a/src/Internal/FutureIterator.php
+++ b/src/Internal/FutureIterator.php
@@ -3,6 +3,8 @@
 namespace Amp\Internal;
 
 use Amp\Cancellation;
+use Amp\ForbidCloning;
+use Amp\ForbidSerialization;
 use Amp\Future;
 use Amp\NullCancellation;
 use Revolt\EventLoop;
@@ -15,6 +17,9 @@
  */
 final class FutureIterator
 {
+    use ForbidCloning;
+    use ForbidSerialization;
+
     /**
      * @var FutureIteratorQueue<Tk, Tv>
      */
diff --git a/src/Internal/WrappedCancellation.php b/src/Internal/WrappedCancellation.php
index f6a575e8..bdf1d375 100644
--- a/src/Internal/WrappedCancellation.php
+++ b/src/Internal/WrappedCancellation.php
@@ -3,12 +3,17 @@
 namespace Amp\Internal;
 
 use Amp\Cancellation;
+use Amp\ForbidCloning;
+use Amp\ForbidSerialization;
 
 /**
  * @internal
  */
 final class WrappedCancellation implements Cancellation
 {
+    use ForbidCloning;
+    use ForbidSerialization;
+
     public function __construct(
         private readonly Cancellation $cancellation
     ) {
diff --git a/src/TimeoutCancellation.php b/src/TimeoutCancellation.php
index 2eff9c05..21eb0092 100644
--- a/src/TimeoutCancellation.php
+++ b/src/TimeoutCancellation.php
@@ -9,6 +9,9 @@
  */
 final class TimeoutCancellation implements Cancellation
 {
+    use ForbidCloning;
+    use ForbidSerialization;
+
     private readonly string $watcher;
 
     private readonly Cancellation $cancellation;
diff --git a/test/Cancellation/CompositeCancellationTest.php b/test/Cancellation/CompositeCancellationTest.php
index 8688e19f..86bda023 100644
--- a/test/Cancellation/CompositeCancellationTest.php
+++ b/test/Cancellation/CompositeCancellationTest.php
@@ -34,7 +34,7 @@ public function testBenchmark(): void
 
             // Asserts
             if ($firstMemoryMeasure > 0) {
-                self::assertEquals($firstMemoryMeasure, \memory_get_usage(true));
+                self::assertLessThanOrEqual($firstMemoryMeasure, \memory_get_usage(true));
             }
         }
     }