diff --git a/src/Type/Definition/Config.php b/src/Type/Definition/Config.php
index 815b8c6..0d1a171 100644
--- a/src/Type/Definition/Config.php
+++ b/src/Type/Definition/Config.php
@@ -19,6 +19,7 @@ class Config
     const SCALAR = 32;
     const CALLBACK = 64;
     const ANY = 128;
+    const NAME = 256;
 
     const OUTPUT_TYPE = 2048;
     const INPUT_TYPE = 4096;
@@ -253,6 +254,13 @@ class Config
                 case $def & self::SCALAR:
                     Utils::invariant(is_scalar($value), $err, 'scalar');
                     break;
+                case $def & self::NAME:
+                    Utils::invariant(
+                        preg_match('~^[_a-zA-Z][_a-zA-Z0-9]*$~', $value),
+                        'Names must match /^[_a-zA-Z][_a-zA-Z0-9]*$/ but "%s" does not.',
+                        $value
+                    );
+                    break;
                 case $def & self::INPUT_TYPE:
                     Utils::invariant(
                         is_callable($value) || $value instanceof InputType,
diff --git a/src/Type/Definition/EnumType.php b/src/Type/Definition/EnumType.php
index cb71a91..2945a50 100644
--- a/src/Type/Definition/EnumType.php
+++ b/src/Type/Definition/EnumType.php
@@ -32,9 +32,9 @@ class EnumType extends Type implements InputType, OutputType, LeafType
         }
 
         Config::validate($config, [
-            'name' => Config::STRING | Config::REQUIRED,
+            'name' => Config::NAME | Config::REQUIRED,
             'values' => Config::arrayOf([
-                'name' => Config::STRING | Config::REQUIRED,
+                'name' => Config::NAME | Config::REQUIRED,
                 'value' => Config::ANY,
                 'deprecationReason' => Config::STRING,
                 'description' => Config::STRING
diff --git a/src/Type/Definition/FieldDefinition.php b/src/Type/Definition/FieldDefinition.php
index 0fe06f5..650d9dd 100644
--- a/src/Type/Definition/FieldDefinition.php
+++ b/src/Type/Definition/FieldDefinition.php
@@ -73,10 +73,10 @@ class FieldDefinition
     public static function getDefinition()
     {
         return self::$def ?: (self::$def = [
-            'name' => Config::STRING | Config::REQUIRED,
+            'name' => Config::NAME | Config::REQUIRED,
             'type' => Config::OUTPUT_TYPE | Config::REQUIRED,
             'args' => Config::arrayOf([
-                'name' => Config::STRING | Config::REQUIRED,
+                'name' => Config::NAME | Config::REQUIRED,
                 'type' => Config::INPUT_TYPE | Config::REQUIRED,
                 'description' => Config::STRING,
                 'defaultValue' => Config::ANY
diff --git a/src/Type/Definition/InputObjectType.php b/src/Type/Definition/InputObjectType.php
index cf32a79..322a51a 100644
--- a/src/Type/Definition/InputObjectType.php
+++ b/src/Type/Definition/InputObjectType.php
@@ -30,9 +30,9 @@ class InputObjectType extends Type implements InputType
         }
 
         Config::validate($config, [
-            'name' => Config::STRING | Config::REQUIRED,
+            'name' => Config::NAME | Config::REQUIRED,
             'fields' => Config::arrayOf([
-                'name' => Config::STRING | Config::REQUIRED,
+                'name' => Config::NAME | Config::REQUIRED,
                 'type' => Config::INPUT_TYPE | Config::REQUIRED,
                 'defaultValue' => Config::ANY,
                 'description' => Config::STRING
diff --git a/src/Type/Definition/InterfaceType.php b/src/Type/Definition/InterfaceType.php
index 126a597..410de70 100644
--- a/src/Type/Definition/InterfaceType.php
+++ b/src/Type/Definition/InterfaceType.php
@@ -40,7 +40,7 @@ class InterfaceType extends Type implements AbstractType, OutputType, CompositeT
         }
 
         Config::validate($config, [
-            'name' => Config::STRING,
+            'name' => Config::NAME,
             'fields' => Config::arrayOf(
                 FieldDefinition::getDefinition(),
                 Config::KEY_AS_NAME | Config::MAYBE_THUNK | Config::MAYBE_TYPE
diff --git a/src/Type/Definition/ObjectType.php b/src/Type/Definition/ObjectType.php
index 25c4037..134a248 100644
--- a/src/Type/Definition/ObjectType.php
+++ b/src/Type/Definition/ObjectType.php
@@ -88,7 +88,7 @@ class ObjectType extends Type implements OutputType, CompositeType
         // Note: this validation is disabled by default, because it is resource-consuming
         // TODO: add bin/validate script to check if schema is valid during development
         Config::validate($config, [
-            'name' => Config::STRING | Config::REQUIRED,
+            'name' => Config::NAME | Config::REQUIRED,
             'fields' => Config::arrayOf(
                 FieldDefinition::getDefinition(),
                 Config::KEY_AS_NAME | Config::MAYBE_THUNK | Config::MAYBE_TYPE
diff --git a/src/Type/Definition/UnionType.php b/src/Type/Definition/UnionType.php
index 74ab9be..e113986 100644
--- a/src/Type/Definition/UnionType.php
+++ b/src/Type/Definition/UnionType.php
@@ -41,7 +41,7 @@ class UnionType extends Type implements AbstractType, OutputType, CompositeType
         }
 
         Config::validate($config, [
-            'name' => Config::STRING | Config::REQUIRED,
+            'name' => Config::NAME | Config::REQUIRED,
             'types' => Config::arrayOf(Config::OBJECT_TYPE, Config::MAYBE_THUNK | Config::REQUIRED),
             'resolveType' => Config::CALLBACK, // function($value, ResolveInfo $info) => ObjectType
             'description' => Config::STRING