diff --git a/src/Type/Definition/Config.php b/src/Type/Definition/Config.php
index 69ba068..e2b5660 100644
--- a/src/Type/Definition/Config.php
+++ b/src/Type/Definition/Config.php
@@ -21,6 +21,7 @@ class Config
 
     const REQUIRED = 65536;
     const KEY_AS_NAME = 131072;
+    const MAYBE_THUNK = 262144;
 
     private static $enableValidation = false;
 
@@ -105,7 +106,11 @@ class Config
             if ($def->flags & self::REQUIRED === 0 && $value === null) {
                 return ;
             }
-            Utils::invariant(is_array($value), $err, 'array');
+            if (($def->flags & self::MAYBE_THUNK) > 0) {
+                Utils::invariant(is_array($value) || is_callable($value), $err, 'array or callable');
+            } else {
+                Utils::invariant(is_array($value), $err, 'array');
+            }
 
             if (!empty($def->isMap)) {
                 if ($def->flags & self::KEY_AS_NAME) {
diff --git a/src/Type/Definition/InputObjectType.php b/src/Type/Definition/InputObjectType.php
index 88de86e..d5cdb4f 100644
--- a/src/Type/Definition/InputObjectType.php
+++ b/src/Type/Definition/InputObjectType.php
@@ -21,7 +21,7 @@ class InputObjectType extends Type implements InputType
                 'type' => Config::INPUT_TYPE | Config::REQUIRED,
                 'defaultValue' => Config::ANY,
                 'description' => Config::STRING
-            ], Config::KEY_AS_NAME),
+            ], Config::KEY_AS_NAME | Config::MAYBE_THUNK),
             'description' => Config::STRING
         ]);
 
diff --git a/src/Type/Definition/InterfaceType.php b/src/Type/Definition/InterfaceType.php
index c7e470c..5192149 100644
--- a/src/Type/Definition/InterfaceType.php
+++ b/src/Type/Definition/InterfaceType.php
@@ -55,7 +55,7 @@ class InterfaceType extends Type implements AbstractType, OutputType, CompositeT
             'name' => Config::STRING,
             'fields' => Config::arrayOf(
                 FieldDefinition::getDefinition(),
-                Config::KEY_AS_NAME
+                Config::KEY_AS_NAME | Config::MAYBE_THUNK
             ),
             'resolveType' => Config::CALLBACK, // function($value, ResolveInfo $info) => ObjectType
             'description' => Config::STRING
diff --git a/src/Type/Definition/ObjectType.php b/src/Type/Definition/ObjectType.php
index 5fd211b..675bcce 100644
--- a/src/Type/Definition/ObjectType.php
+++ b/src/Type/Definition/ObjectType.php
@@ -79,11 +79,12 @@ class ObjectType extends Type implements OutputType, CompositeType
             'name' => Config::STRING | Config::REQUIRED,
             'fields' => Config::arrayOf(
                 FieldDefinition::getDefinition(),
-                Config::KEY_AS_NAME
+                Config::KEY_AS_NAME | Config::MAYBE_THUNK
             ),
             'description' => Config::STRING,
             'interfaces' => Config::arrayOf(
-                Config::INTERFACE_TYPE
+                Config::INTERFACE_TYPE,
+                Config::MAYBE_THUNK
             ),
             'isTypeOf' => Config::CALLBACK, // ($value, ResolveInfo $info) => boolean
             'resolveField' => Config::CALLBACK