diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 57422de5..a13804b5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -11,6 +11,7 @@ jobs:
     strategy:
       matrix:
         php:
+          - 8.0
           - 7.4
           - 7.3
           - 7.2
diff --git a/src/functions.php b/src/functions.php
index bdbdf52d..68763db3 100644
--- a/src/functions.php
+++ b/src/functions.php
@@ -341,11 +341,43 @@ function _checkTypehint(callable $callback, $object)
         return true;
     }
 
-    $expectedException = $parameters[0];
+    if (\PHP_VERSION_ID < 70100 || \defined('HHVM_VERSION')) {
+        $expectedException = $parameters[0];
 
-    if (!$expectedException->getClass()) {
-        return true;
-    }
+        if (!$expectedException->getClass()) {
+            return true;
+        }
+
+        return $expectedException->getClass()->isInstance($object);
+    } else {
+        $type = $parameters[0]->getType();
 
-    return $expectedException->getClass()->isInstance($object);
+        if (!$type) {
+            return true;
+        }
+
+        $types = [$type];
+
+        if ($type instanceof \ReflectionUnionType) {
+            $types = $type->getTypes();
+        }
+
+        $mismatched = false;
+
+        foreach ($types as $type) {
+            if (!$type || $type->isBuiltin()) {
+                continue;
+            }
+
+            $expectedClass = $type->getName();
+
+            if ($object instanceof $expectedClass) {
+                return true;
+            }
+
+            $mismatched = true;
+        }
+
+        return !$mismatched;
+    }
 }
diff --git a/tests/FunctionCheckTypehintTest.php b/tests/FunctionCheckTypehintTest.php
index 8449bc1f..5c78ab36 100644
--- a/tests/FunctionCheckTypehintTest.php
+++ b/tests/FunctionCheckTypehintTest.php
@@ -23,22 +23,65 @@ public function shouldAcceptFunctionStringCallbackWithTypehint()
     /** @test */
     public function shouldAcceptInvokableObjectCallbackWithTypehint()
     {
-        $this->assertTrue(_checkTypehint(new TestCallbackWithTypehintClass(), new \InvalidArgumentException()));
-        $this->assertfalse(_checkTypehint(new TestCallbackWithTypehintClass(), new \Exception()));
+        $this->assertTrue(_checkTypehint(new CallbackWithTypehintClass(), new \InvalidArgumentException()));
+        $this->assertfalse(_checkTypehint(new CallbackWithTypehintClass(), new \Exception()));
     }
 
     /** @test */
     public function shouldAcceptObjectMethodCallbackWithTypehint()
     {
-        $this->assertTrue(_checkTypehint([new TestCallbackWithTypehintClass(), 'testCallback'], new \InvalidArgumentException()));
-        $this->assertfalse(_checkTypehint([new TestCallbackWithTypehintClass(), 'testCallback'], new \Exception()));
+        $this->assertTrue(_checkTypehint([new CallbackWithTypehintClass(), 'testCallback'], new \InvalidArgumentException()));
+        $this->assertfalse(_checkTypehint([new CallbackWithTypehintClass(), 'testCallback'], new \Exception()));
     }
 
     /** @test */
     public function shouldAcceptStaticClassCallbackWithTypehint()
     {
-        $this->assertTrue(_checkTypehint(['React\Promise\TestCallbackWithTypehintClass', 'testCallbackStatic'], new \InvalidArgumentException()));
-        $this->assertfalse(_checkTypehint(['React\Promise\TestCallbackWithTypehintClass', 'testCallbackStatic'], new \Exception()));
+        $this->assertTrue(_checkTypehint([new CallbackWithTypehintClass(), 'testCallbackStatic'], new \InvalidArgumentException()));
+        $this->assertfalse(_checkTypehint([new CallbackWithTypehintClass(), 'testCallbackStatic'], new \Exception()));
+    }
+
+    /**
+     * @test
+     * @requires PHP 8
+     */
+    public function shouldAcceptClosureCallbackWithUnionTypehint()
+    {
+        eval(
+            'namespace React\Promise;' .
+            'self::assertTrue(_checkTypehint(function (\RuntimeException|\InvalidArgumentException $e) {}, new \InvalidArgumentException()));' .
+            'self::assertFalse(_checkTypehint(function (\RuntimeException|\InvalidArgumentException $e) {}, new \Exception()));'
+        );
+    }
+
+    /**
+     * @test
+     * @requires PHP 8
+     */
+    public function shouldAcceptInvokableObjectCallbackWithUnionTypehint()
+    {
+        self::assertTrue(_checkTypehint(new CallbackWithUnionTypehintClass(), new \InvalidArgumentException()));
+        self::assertFalse(_checkTypehint(new CallbackWithUnionTypehintClass(), new \Exception()));
+    }
+
+    /**
+     * @test
+     * @requires PHP 8
+     */
+    public function shouldAcceptObjectMethodCallbackWithUnionTypehint()
+    {
+        self::assertTrue(_checkTypehint([new CallbackWithUnionTypehintClass(), 'testCallback'], new \InvalidArgumentException()));
+        self::assertFalse(_checkTypehint([new CallbackWithUnionTypehintClass(), 'testCallback'], new \Exception()));
+    }
+
+    /**
+     * @test
+     * @requires PHP 8
+     */
+    public function shouldAcceptStaticClassCallbackWithUnionTypehint()
+    {
+        self::assertTrue(_checkTypehint(['React\Promise\CallbackWithUnionTypehintClass', 'testCallbackStatic'], new \InvalidArgumentException()));
+        self::assertFalse(_checkTypehint(['React\Promise\CallbackWithUnionTypehintClass', 'testCallbackStatic'], new \Exception()));
     }
 
     /** @test */
@@ -57,19 +100,19 @@ public function shouldAcceptFunctionStringCallbackWithoutTypehint()
     /** @test */
     public function shouldAcceptInvokableObjectCallbackWithoutTypehint()
     {
-        $this->assertTrue(_checkTypehint(new TestCallbackWithoutTypehintClass(), new \InvalidArgumentException()));
+        $this->assertTrue(_checkTypehint(new CallbackWithoutTypehintClass(), new \InvalidArgumentException()));
     }
 
     /** @test */
     public function shouldAcceptObjectMethodCallbackWithoutTypehint()
     {
-        $this->assertTrue(_checkTypehint([new TestCallbackWithoutTypehintClass(), 'testCallback'], new \InvalidArgumentException()));
+        $this->assertTrue(_checkTypehint([new CallbackWithoutTypehintClass(), 'testCallback'], new \InvalidArgumentException()));
     }
 
     /** @test */
     public function shouldAcceptStaticClassCallbackWithoutTypehint()
     {
-        $this->assertTrue(_checkTypehint(['React\Promise\TestCallbackWithoutTypehintClass', 'testCallbackStatic'], new \InvalidArgumentException()));
+        $this->assertTrue(_checkTypehint(['React\Promise\CallbackWithoutTypehintClass', 'testCallbackStatic'], new \InvalidArgumentException()));
     }
 }
 
@@ -80,39 +123,3 @@ function testCallbackWithTypehint(\InvalidArgumentException $e)
 function testCallbackWithoutTypehint()
 {
 }
-
-class TestCallbackWithTypehintClass
-{
-    public function __invoke(\InvalidArgumentException $e)
-    {
-
-    }
-
-    public function testCallback(\InvalidArgumentException $e)
-    {
-
-    }
-
-    public static function testCallbackStatic(\InvalidArgumentException $e)
-    {
-
-    }
-}
-
-class TestCallbackWithoutTypehintClass
-{
-    public function __invoke()
-    {
-
-    }
-
-    public function testCallback()
-    {
-
-    }
-
-    public static function testCallbackStatic()
-    {
-
-    }
-}
diff --git a/tests/fixtures/CallbackWithTypehintClass.php b/tests/fixtures/CallbackWithTypehintClass.php
new file mode 100644
index 00000000..12dd0da4
--- /dev/null
+++ b/tests/fixtures/CallbackWithTypehintClass.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace React\Promise;
+
+use InvalidArgumentException;
+
+class CallbackWithTypehintClass
+{
+    public function __invoke(InvalidArgumentException $e)
+    {
+    }
+
+    public function testCallback(InvalidArgumentException $e)
+    {
+    }
+
+    public static function testCallbackStatic(InvalidArgumentException $e)
+    {
+    }
+}
diff --git a/tests/fixtures/CallbackWithUnionTypehintClass.php b/tests/fixtures/CallbackWithUnionTypehintClass.php
new file mode 100644
index 00000000..4c195fe2
--- /dev/null
+++ b/tests/fixtures/CallbackWithUnionTypehintClass.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace React\Promise;
+
+use InvalidArgumentException;
+use RuntimeException;
+
+class CallbackWithUnionTypehintClass
+{
+    public function __invoke(RuntimeException|InvalidArgumentException $e)
+    {
+    }
+
+    public function testCallback(RuntimeException|InvalidArgumentException $e)
+    {
+    }
+
+    public static function testCallbackStatic(RuntimeException|InvalidArgumentException $e)
+    {
+    }
+}
diff --git a/tests/fixtures/CallbackWithoutTypehintClass.php b/tests/fixtures/CallbackWithoutTypehintClass.php
new file mode 100644
index 00000000..618aeebe
--- /dev/null
+++ b/tests/fixtures/CallbackWithoutTypehintClass.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace React\Promise;
+
+class CallbackWithoutTypehintClass
+{
+    public function __invoke()
+    {
+    }
+
+    public function testCallback()
+    {
+    }
+
+    public static function testCallbackStatic()
+    {
+    }
+}