diff --git a/README.md b/README.md
index 239ca67..737f158 100644
--- a/README.md
+++ b/README.md
@@ -93,7 +93,17 @@ Every time you call `Yard\Data\PostData::from($post)` you receive an instance of
 
 If you choose to create a new data class for your custom post type, you can have this class be returned for all instances of that post type.
 
-Just use the config file and map all custom posts and it's classes:
+To do this, you need to add the Fully Qualified Class Name (FQCN) of your custom data class to the `supports` array when registering your custom post type:
+
+```php
+register_post_type('vacancy', [
+    'supports' => [
+        'data-class' => ['classFQN' => App\Data\KnowledgebaseData::class],
+    ],
+]);
+````
+
+Another option is to create a mapping in the `config/yard-data.php` file. The mapping in the project config takes precedence over the register_post_type `supports` args.
 
 ```php
 'post_types' => [
diff --git a/src/PostData.php b/src/PostData.php
index c508f18..8f6efc1 100644
--- a/src/PostData.php
+++ b/src/PostData.php
@@ -8,6 +8,7 @@
 use Corcel\Model\Post;
 use ReflectionClass;
 use ReflectionNamedType;
+use RuntimeException;
 use Spatie\LaravelData\Attributes\MapInputName;
 use Spatie\LaravelData\Attributes\WithCastable;
 use Spatie\LaravelData\Data;
@@ -86,7 +87,7 @@ public static function fromCorcel(Post $post): PostData
 	}
 
 	/**
-	 * @return class-string<self>
+	 * @return class-string<PostData>
 	 */
 	private static function dataClass(string $postType): string
 	{
@@ -96,7 +97,21 @@ private static function dataClass(string $postType): string
 			return $classes[$postType];
 		}
 
-		return static::class;
+		$classFQN = get_all_post_type_supports($postType)['data-class'][0]['classFQN'] ?? null;
+
+		if (null === $classFQN) {
+			return static::class;
+		}
+		
+		if (! class_exists($classFQN)) {
+			throw new RuntimeException(sprintf('The class "%s" does not exist or is not autoloaded.', $classFQN));
+		}
+
+		if (! is_a($classFQN, PostData::class, true)) {
+			throw new RuntimeException(sprintf('The class "%s" must extend %s.', $classFQN, PostData::class));
+		}
+
+		return $classFQN;
 	}
 
 	private function metaPrefix(): string