diff --git a/src/Type/Schema.php b/src/Type/Schema.php
index dfdebb5..b4ec795 100644
--- a/src/Type/Schema.php
+++ b/src/Type/Schema.php
@@ -110,7 +110,6 @@ class Schema
         );
 
         $this->config = $config;
-        $this->resolvedTypes = Type::getInternalTypes() + Introspection::getTypes();
         $this->resolvedTypes[$config->query->name] = $config->query;
 
         if ($config->mutation) {
@@ -119,6 +118,20 @@ class Schema
         if ($config->subscription) {
             $this->resolvedTypes[$config->subscription->name] = $config->subscription;
         }
+        if (is_array($this->config->types)) {
+            foreach ($this->resolveAdditionalTypes() as $type) {
+                if (isset($this->resolvedTypes[$type->name])) {
+                    Utils::invariant(
+                        $type === $this->resolvedTypes[$type->name],
+                        "Schema must contain unique named types but contains multiple types named \"$type\" ".
+                        "(see http://webonyx.github.io/graphql-php/type-system/#type-registry)."
+                    );
+                }
+                $this->resolvedTypes[$type->name] = $type;
+            }
+        }
+        $this->resolvedTypes += Type::getInternalTypes() + Introspection::getTypes();
+
         if (!$this->config->typeLoader) {
             // Perform full scan of the schema
             $this->getTypeMap();
@@ -209,8 +222,11 @@ class Schema
         foreach ($this->resolvedTypes as $type) {
             $typeMap = TypeInfo::extractTypes($type, $typeMap);
         }
-        foreach ($this->resolveAdditionalTypes() as $type) {
-            $typeMap = TypeInfo::extractTypes($type, $typeMap);
+        // When types are set as array they are resolved in constructor
+        if (is_callable($this->config->types)) {
+            foreach ($this->resolveAdditionalTypes() as $type) {
+                $typeMap = TypeInfo::extractTypes($type, $typeMap);
+            }
         }
         return $typeMap;
     }
diff --git a/tests/StarWarsIntrospectionTest.php b/tests/StarWarsIntrospectionTest.php
index 530c760..2569027 100644
--- a/tests/StarWarsIntrospectionTest.php
+++ b/tests/StarWarsIntrospectionTest.php
@@ -26,8 +26,13 @@ class StarWarsIntrospectionTest extends \PHPUnit_Framework_TestCase
         $expected = [
             '__schema' => [
                 'types' => [
-                    ['name' => 'ID'],
+                    ['name' => 'Query'],
+                    ['name' => 'Episode'],
+                    ['name' => 'Character'],
                     ['name' => 'String'],
+                    ['name' => 'Human'],
+                    ['name' => 'Droid'],
+                    ['name' => 'ID'],
                     ['name' => 'Float'],
                     ['name' => 'Int'],
                     ['name' => 'Boolean'],
@@ -39,11 +44,6 @@ class StarWarsIntrospectionTest extends \PHPUnit_Framework_TestCase
                     ['name' => '__EnumValue'],
                     ['name' => '__Directive'],
                     ['name' => '__DirectiveLocation'],
-                    ['name' => 'Query'],
-                    ['name' => 'Episode'],
-                    ['name' => 'Character'],
-                    ['name' => 'Human'],
-                    ['name' => 'Droid'],
                 ]
             ]
         ];
diff --git a/tests/Type/DefinitionTest.php b/tests/Type/DefinitionTest.php
index 86439e1..f0f3fe3 100644
--- a/tests/Type/DefinitionTest.php
+++ b/tests/Type/DefinitionTest.php
@@ -3,6 +3,7 @@ namespace GraphQL\Tests\Type;
 
 require_once __DIR__ . '/TestClasses.php';
 
+use GraphQL\Type\Definition\CustomScalarType;
 use GraphQL\Type\Schema;
 use GraphQL\Type\Definition\EnumType;
 use GraphQL\Type\Definition\InputObjectType;
@@ -713,5 +714,21 @@ class DefinitionTest extends \PHPUnit_Framework_TestCase
         $otherCustom = new OtherCustom();
         $this->assertEquals('OtherCustom', $otherCustom->name);
     }
-}
 
+    public function testAllowsOverridingInternalTypes()
+    {
+        $idType = new CustomScalarType([
+            'name' => 'ID',
+            'serialize' => function() {},
+            'parseValue' => function() {},
+            'parseLiteral' => function() {}
+        ]);
+
+        $schema = new Schema([
+            'query' => new ObjectType(['name' => 'Query', 'fields' => []]),
+            'types' => [$idType]
+        ]);
+
+        $this->assertSame($idType, $schema->getType('ID'));
+    }
+}
diff --git a/tests/Type/IntrospectionTest.php b/tests/Type/IntrospectionTest.php
index 54a00d7..532028b 100644
--- a/tests/Type/IntrospectionTest.php
+++ b/tests/Type/IntrospectionTest.php
@@ -42,9 +42,32 @@ class IntrospectionTest extends \PHPUnit_Framework_TestCase
                                 ),
                             'types' =>
                                 array (
+                                    array (
+                                        'kind' => 'OBJECT',
+                                        'name' => 'QueryRoot',
+                                        'inputFields' => NULL,
+                                        'interfaces' =>
+                                            array (
+                                            ),
+                                        'enumValues' => NULL,
+                                        'possibleTypes' => NULL,
+                                        'fields' => array (
+                                            array (
+                                                'name' => 'a',
+                                                'args' => array(),
+                                                'type' => array(
+                                                    'kind' => 'SCALAR',
+                                                    'name' => 'String',
+                                                    'ofType' => null
+                                                ),
+                                                'isDeprecated' => false,
+                                                'deprecationReason' => null,
+                                            )
+                                        )
+                                    ),
                                     array (
                                         'kind' => 'SCALAR',
-                                        'name' => 'ID',
+                                        'name' => 'String',
                                         'fields' => NULL,
                                         'inputFields' => NULL,
                                         'interfaces' => NULL,
@@ -53,7 +76,7 @@ class IntrospectionTest extends \PHPUnit_Framework_TestCase
                                     ),
                                     array (
                                         'kind' => 'SCALAR',
-                                        'name' => 'String',
+                                        'name' => 'ID',
                                         'fields' => NULL,
                                         'inputFields' => NULL,
                                         'interfaces' => NULL,
@@ -975,29 +998,6 @@ class IntrospectionTest extends \PHPUnit_Framework_TestCase
                                             ),
                                         'possibleTypes' => NULL,
                                     ),
-                                    array (
-                                        'kind' => 'OBJECT',
-                                        'name' => 'QueryRoot',
-                                        'inputFields' => NULL,
-                                        'interfaces' =>
-                                            array (
-                                            ),
-                                        'enumValues' => NULL,
-                                        'possibleTypes' => NULL,
-                                        'fields' => array (
-                                            array (
-                                                'name' => 'a',
-                                                'args' => array(),
-                                                'type' => array(
-                                                    'kind' => 'SCALAR',
-                                                    'name' => 'String',
-                                                    'ofType' => null
-                                                ),
-                                                'isDeprecated' => false,
-                                                'deprecationReason' => null,
-                                            )
-                                        )
-                                    ),
                                 ),
                             'directives' =>
                                 array (