diff --git a/CHANGELOG.md b/CHANGELOG.md
index 58e75fff7..96d9b598c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,9 @@
 
 ### vNEXT
 
+### v0.9.9
+- fix issue with @types/graphql@0.13
+
 ### v0.9.8
 - added `error` event to handle connection errors and debug network troubles [PR #341](https://github.com/apollographql/subscriptions-transport-ws/pull/341).
 - added feature inactivityTimeout [PR #390](https://github.com/apollographql/subscriptions-transport-ws/pull/390)
diff --git a/package.json b/package.json
index 3c2b671f7..650680f8a 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "subscriptions-transport-ws",
-  "version": "0.9.8",
+  "version": "0.9.9",
   "description": "A websocket transport for GraphQL subscriptions",
   "main": "dist/index.js",
   "browser": "dist/client.js",
@@ -37,7 +37,7 @@
   },
   "devDependencies": {
     "@types/chai": "^4.0.0",
-    "@types/graphql": "^0.11.3",
+    "@types/graphql": "^0.13.0",
     "@types/is-promise": "^2.1.0",
     "@types/lodash": "^4.14.68",
     "@types/mocha": "^2.2.41",
@@ -45,7 +45,7 @@
     "@types/sinon": "^2.3.0",
     "@types/ws": "^3.0.0",
     "chai": "^4.0.2",
-    "graphql": "^0.13.1",
+    "graphql": "^0.13.2",
     "graphql-subscriptions": "^0.5.7",
     "istanbul": "^1.0.0-alpha.2",
     "lodash": "^4.17.1",
@@ -53,8 +53,8 @@
     "remap-istanbul": "^0.9.5",
     "rimraf": "^2.6.1",
     "sinon": "^2.3.6",
-    "tslint": "^5.8.0",
-    "typescript": "^2.6.2",
+    "tslint": "^5.10.0",
+    "typescript": "^2.8.3",
     "webpack": "^3.1.0"
   },
   "typings": "dist/index.d.ts",
diff --git a/src/server.ts b/src/server.ts
index c2cf01033..569b6b6a9 100644
--- a/src/server.ts
+++ b/src/server.ts
@@ -61,6 +61,7 @@ export type ExecuteFunction = (schema: GraphQLSchema,
                                variableValues?: { [key: string]: any },
                                operationName?: string,
                                fieldResolver?: GraphQLFieldResolver<any, any>) =>
+                               ExecutionResult |
                                Promise<ExecutionResult> |
                                AsyncIterator<ExecutionResult>;
 
@@ -332,7 +333,7 @@ export class SubscriptionServer {
 
               const document = typeof baseParams.query !== 'string' ? baseParams.query : parse(baseParams.query);
               let executionPromise: Promise<AsyncIterator<ExecutionResult> | ExecutionResult>;
-              const validationErrors: Error[] = validate(this.schema, document, this.specifiedRules);
+              const validationErrors = validate(this.schema, document, this.specifiedRules);
 
               if ( validationErrors.length > 0 ) {
                 executionPromise = Promise.resolve({ errors: validationErrors });