diff --git a/src/CreateDescriptor.php b/src/CreateDescriptor.php
index 69d4a692..1c2586c6 100644
--- a/src/CreateDescriptor.php
+++ b/src/CreateDescriptor.php
@@ -6,6 +6,7 @@
 
 use Koriym\AppStateDiagram\Exception\DescriptorIsNotArrayException;
 use Koriym\AppStateDiagram\Exception\InvalidDescriptorException;
+use Koriym\AppStateDiagram\Exception\InvalidTypeException;
 use stdClass;
 
 use function assert;
@@ -18,6 +19,8 @@
 
 final class CreateDescriptor
 {
+    private const VALID_TYPES = ['semantic', 'safe', 'unsafe', 'idempotent'];
+
     /**
      * @param array<string, stdClass> $descriptorsArray
      *
@@ -118,5 +121,9 @@ private function validateDescriptor(stdClass $descriptor): void
         if ($hasNoId) {
             throw new InvalidDescriptorException((string) json_encode($descriptor));
         }
+
+        if (isset($descriptor->type) && ! in_array($descriptor->type, self::VALID_TYPES)) {
+            throw new InvalidTypeException((string) $descriptor->type);
+        }
     }
 }
diff --git a/src/Exception/InvalidTypeException.php b/src/Exception/InvalidTypeException.php
new file mode 100644
index 00000000..aebe83cf
--- /dev/null
+++ b/src/Exception/InvalidTypeException.php
@@ -0,0 +1,11 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Koriym\AppStateDiagram\Exception;
+
+use RuntimeException;
+
+class InvalidTypeException extends RuntimeException
+{
+}
diff --git a/tests/CreateDescriptorTest.php b/tests/CreateDescriptorTest.php
new file mode 100644
index 00000000..72f6ec43
--- /dev/null
+++ b/tests/CreateDescriptorTest.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Koriym\AppStateDiagram;
+
+use Koriym\AppStateDiagram\Exception\InvalidTypeException;
+use PHPUnit\Framework\TestCase;
+use stdClass;
+
+class CreateDescriptorTest extends TestCase
+{
+    public function testInvalidType(): void
+    {
+        $this->expectException(InvalidTypeException::class);
+        $stdClass = new stdClass();
+        $stdClass->id = 'About';
+        $stdClass->type = '_invalid_';
+        $instances = ['About' => $stdClass];
+        (new CreateDescriptor())($instances);
+    }
+}