diff --git a/src/Type/Definition/ScalarType.php b/src/Type/Definition/ScalarType.php
index d93b2e7..db4e63f 100644
--- a/src/Type/Definition/ScalarType.php
+++ b/src/Type/Definition/ScalarType.php
@@ -5,6 +5,7 @@ declare(strict_types=1);
 namespace GraphQL\Type\Definition;
 
 use GraphQL\Language\AST\ScalarTypeDefinitionNode;
+use GraphQL\Language\AST\ScalarTypeExtensionNode;
 use GraphQL\Utils\Utils;
 use function is_string;
 
@@ -31,15 +32,19 @@ abstract class ScalarType extends Type implements OutputType, InputType, LeafTyp
     /** @var ScalarTypeDefinitionNode|null */
     public $astNode;
 
+    /** @var ScalarTypeExtensionNode[] */
+    public $extensionASTNodes;
+
     /**
      * @param mixed[] $config
      */
     public function __construct(array $config = [])
     {
-        $this->name        = $config['name'] ?? $this->tryInferName();
-        $this->description = $config['description'] ?? $this->description;
-        $this->astNode     = $config['astNode'] ?? null;
-        $this->config      = $config;
+        $this->name              = $config['name'] ?? $this->tryInferName();
+        $this->description       = $config['description'] ?? $this->description;
+        $this->astNode           = $config['astNode'] ?? null;
+        $this->extensionASTNodes = $config['extensionASTNodes'] ?? null;
+        $this->config            = $config;
 
         Utils::invariant(is_string($this->name), 'Must provide name.');
     }