diff --git a/lib/Worker/Internal/Job.php b/lib/Worker/Internal/Job.php
index 6dcdc3a..75d3f3f 100644
--- a/lib/Worker/Internal/Job.php
+++ b/lib/Worker/Internal/Job.php
@@ -2,6 +2,7 @@
 
 namespace Amp\Parallel\Worker\Internal;
 
+use Amp\Parallel\Worker\Environment;
 use Amp\Parallel\Worker\Task;
 
 /** @internal */
@@ -23,10 +24,14 @@ class Job {
 
     public function getTask(): Task {
         // Classes that cannot be autoloaded will be unserialized as an instance of __PHP_Incomplete_Class.
-        \assert(
-            $this->task instanceof Task,
-            \sprintf("Classes implementing %s must be autoloadable by the Composer autoloader", Task::class)
-        );
+        if ($this->task instanceof \__PHP_Incomplete_Class) {
+            return new class implements Task {
+                public function run(Environment $environment) {
+                    throw new \Error(\sprintf("Classes implementing %s must be autoloadable by the Composer autoloader", Task::class));
+                }
+            };
+        }
+
         return $this->task;
     }
 }
diff --git a/test/Worker/AbstractWorkerTest.php b/test/Worker/AbstractWorkerTest.php
index 524f6cb..b22f8c7 100644
--- a/test/Worker/AbstractWorkerTest.php
+++ b/test/Worker/AbstractWorkerTest.php
@@ -3,8 +3,17 @@
 namespace Amp\Parallel\Test\Worker;
 
 use Amp\Loop;
+use Amp\Parallel\Worker\Environment;
+use Amp\Parallel\Worker\Task;
+use Amp\Parallel\Worker\TaskError;
 use Amp\PHPUnit\TestCase;
 
+class NonAutoloadableTask implements Task {
+    public function run(Environment $environment) {
+        return 1;
+    }
+}
+
 abstract class AbstractWorkerTest extends TestCase {
     /**
      * @return \Amp\Parallel\Worker\Worker
@@ -93,4 +102,21 @@ abstract class AbstractWorkerTest extends TestCase {
         $this->assertRunTimeLessThan([$worker, 'kill'], 250);
         $this->assertFalse($worker->isRunning());
     }
+
+    public function testUnserializableTask() {
+        Loop::run(function () {
+            $worker = $this->createWorker();
+            $worker->start();
+
+            try {
+                yield $worker->enqueue(new NonAutoloadableTask);
+                $this->fail("Tasks that cannot be autoloaded should throw an exception");
+            } catch (TaskError $exception) {
+                $this->assertSame("Error", $exception->getName());
+                $this->assertGreaterThan(0, \strpos($exception->getMessage(), \sprintf("Classes implementing %s", Task::class)));
+            }
+
+            yield $worker->shutdown();
+        });
+    }
 }