diff --git a/src/Forking/ForkContext.php b/src/Forking/ForkContext.php
index c15922f..2bdb4a4 100644
--- a/src/Forking/ForkContext.php
+++ b/src/Forking/ForkContext.php
@@ -87,7 +87,8 @@ abstract class ForkContext extends Synchronized implements ContextInterface
 
                 // Get the fatal exception from the process.
                 return $this->parentSocket->read(2)->then(function ($data) {
-                    list($serializedLength) = unpack('S', $data);
+                    $serializedLength = unpack('S', $data);
+                    $serializedLength = $serializedLength[1];
                     return $this->parentSocket->read($serializedLength);
                 })->then(function ($data) {
                     $previous = unserialize($data);
@@ -162,4 +163,15 @@ abstract class ForkContext extends Synchronized implements ContextInterface
      * {@inheritdoc}
      */
     abstract public function run();
+
+    public function __destruct()
+    {
+        parent::__destruct();
+
+        // The parent process outlives the child process, so don't destroy the
+        // semaphore until the parent exits.
+        if (!$this->isChild) {
+            $this->semaphore->destroy();
+        }
+    }
 }
diff --git a/src/Forking/Synchronized.php b/src/Forking/Synchronized.php
index b05f024..f75a3a8 100644
--- a/src/Forking/Synchronized.php
+++ b/src/Forking/Synchronized.php
@@ -15,7 +15,7 @@ abstract class Synchronized
 {
     private $memoryBlock;
     private $memoryKey;
-    private $semaphore;
+    protected $semaphore;
 
     /**
      * Creates a new synchronized object.