diff --git a/src/type/schema.js b/src/type/schema.js
index d5526443a09..2ee4df6d119 100644
--- a/src/type/schema.js
+++ b/src/type/schema.js
@@ -13,6 +13,7 @@ import {
   isUnionType,
   isInputObjectType,
   isWrappingType,
+  getNamedType,
 } from './definition';
 import type {
   GraphQLType,
@@ -22,7 +23,11 @@ import type {
   GraphQLInterfaceType,
 } from './definition';
 import type { SchemaDefinitionNode } from '../language/ast';
-import { GraphQLDirective, specifiedDirectives } from './directives';
+import {
+  GraphQLDirective,
+  isDirective,
+  specifiedDirectives,
+} from './directives';
 import type { GraphQLError } from '../error/GraphQLError';
 import { __Schema } from './introspection';
 import find from '../jsutils/find';
@@ -121,6 +126,10 @@ export class GraphQLSchema {
       initialTypes = initialTypes.concat(types);
     }
 
+    initialTypes = initialTypes.concat(
+      ...this._directives.map(directive => getDirectiveArgTypes(directive)),
+    );
+
     this._typeMap = initialTypes.reduce(
       typeMapReducer,
       (Object.create(null): TypeMap),
@@ -269,3 +278,10 @@ function typeMapReducer(map: TypeMap, type: ?GraphQLType): TypeMap {
 
   return reducedMap;
 }
+
+function getDirectiveArgTypes(directive: GraphQLDirective) {
+  if (!isDirective(directive)) {
+    return [];
+  }
+  return directive.args.map(arg => getNamedType(arg.type));
+}