diff --git a/src/Client.ts b/src/Client.ts
index 57618e2..76ce0f4 100644
--- a/src/Client.ts
+++ b/src/Client.ts
@@ -78,7 +78,7 @@ class Client implements IClient {
     if (this.requestManager.connectPromise) {
       await this.requestManager.connectPromise;
     }
-    return this.requestManager.request(requestObject, true);
+    return this.requestManager.request(requestObject, true, null);
   }
 
   public onNotification(callback: (data: IJSONRPCNotification) => void) {
diff --git a/src/RequestManager.ts b/src/RequestManager.ts
index 348f699..7b2aa5d 100644
--- a/src/RequestManager.ts
+++ b/src/RequestManager.ts
@@ -44,7 +44,7 @@ class RequestManager {
     return this.transports[0];
   }
 
-  public async request(requestObject: JSONRPCMessage, notification: boolean = false, timeout?: number): Promise<any> {
+  public async request(requestObject: JSONRPCMessage, notification: boolean = false, timeout?: number | null): Promise<any> {
     const internalID = (++this.lastId).toString();
     const id = notification ? null : internalID;
     // naively grab first transport and use it
diff --git a/src/transports/EventEmitterTransport.ts b/src/transports/EventEmitterTransport.ts
index 5b5271b..9583581 100644
--- a/src/transports/EventEmitterTransport.ts
+++ b/src/transports/EventEmitterTransport.ts
@@ -22,7 +22,7 @@ class EventEmitterTransport extends Transport {
     return Promise.resolve();
   }
 
-  public sendData(data: JSONRPCRequestData, timeout?: number): Promise<any> {
+  public sendData(data: JSONRPCRequestData, timeout: number | null = null): Promise<any> {
     const prom = this.transportRequestManager.addRequest(data, timeout);
     const notifications = getNotifications(data);
     const parsedData = this.parseData(data);
diff --git a/src/transports/HTTPTransport.ts b/src/transports/HTTPTransport.ts
index cf7a4f2..3532bd3 100644
--- a/src/transports/HTTPTransport.ts
+++ b/src/transports/HTTPTransport.ts
@@ -24,7 +24,7 @@ class HTTPTransport extends Transport {
     return Promise.resolve();
   }
 
-  public async sendData(data: JSONRPCRequestData, timeout?: number): Promise<any> {
+  public async sendData(data: JSONRPCRequestData, timeout: number | null = null): Promise<any> {
     const prom = this.transportRequestManager.addRequest(data, timeout);
     const notifications = getNotifications(data);
     const batch = getBatchRequests(data);
diff --git a/src/transports/PostMessageIframeTransport.ts b/src/transports/PostMessageIframeTransport.ts
index e1b94c7..47b4f55 100644
--- a/src/transports/PostMessageIframeTransport.ts
+++ b/src/transports/PostMessageIframeTransport.ts
@@ -45,8 +45,8 @@ class PostMessageIframeTransport extends Transport {
     });
   }
 
-  public async sendData(data: JSONRPCRequestData, timeout: number | undefined = 5000): Promise<any> {
-    const prom = this.transportRequestManager.addRequest(data, undefined);
+  public async sendData(data: JSONRPCRequestData, timeout: number | null = 5000): Promise<any> {
+    const prom = this.transportRequestManager.addRequest(data, null);
     if (this.frame) {
       this.frame.postMessage((data as IJSONRPCData).request, "*");
     }
diff --git a/src/transports/PostMessageWindowTransport.ts b/src/transports/PostMessageWindowTransport.ts
index cc9be8a..00f1905 100644
--- a/src/transports/PostMessageWindowTransport.ts
+++ b/src/transports/PostMessageWindowTransport.ts
@@ -55,7 +55,7 @@ class PostMessageTransport extends Transport {
   }
 
   public async sendData(data: JSONRPCRequestData, timeout: number | undefined = 5000): Promise<any> {
-    const prom = this.transportRequestManager.addRequest(data, undefined);
+    const prom = this.transportRequestManager.addRequest(data, null);
     if (this.frame) {
       this.frame.postMessage((data as IJSONRPCData).request, this.uri);
     }
diff --git a/src/transports/Transport.ts b/src/transports/Transport.ts
index afd44b1..d18d3d2 100644
--- a/src/transports/Transport.ts
+++ b/src/transports/Transport.ts
@@ -30,7 +30,7 @@ export abstract class Transport {
 
   public abstract connect(): Promise<any>;
   public abstract close(): void;
-  public abstract async sendData(data: JSONRPCRequestData, timeout?: number): Promise<any>;
+  public abstract async sendData(data: JSONRPCRequestData, timeout?: number | null): Promise<any>;
 
   public subscribe(event: TransportEventName, handler: ITransportEvents[TransportEventName]) {
     this.transportRequestManager.transportEventChannel.addListener(event, handler);
diff --git a/src/transports/TransportRequestManager.test.ts b/src/transports/TransportRequestManager.test.ts
index 476be94..4f06d07 100644
--- a/src/transports/TransportRequestManager.test.ts
+++ b/src/transports/TransportRequestManager.test.ts
@@ -13,7 +13,7 @@ describe("Transport Request Manager", () => {
       expect(data).toBeDefined();
       done();
     });
-    transportReqMan.addRequest({ request: reqData.generateMockRequest(1, "foo", ["bar"]), internalID: 1 }, undefined);
+    transportReqMan.addRequest({ request: reqData.generateMockRequest(1, "foo", ["bar"]), internalID: 1 }, null);
   });
 
   it("should timeout pending request after 1s", async () => {
@@ -35,7 +35,7 @@ describe("Transport Request Manager", () => {
     // tslint:disable-next-line:no-empty
     const reject = () => { };
     const request: IBatchRequest[] = [{ resolve, reject, request: req }];
-    transportReqMan.addRequest(request, undefined);
+    transportReqMan.addRequest(request, null);
   });
 
   it("should not error on missing id to resolve", () => {
@@ -68,7 +68,7 @@ describe("Transport Request Manager", () => {
 
   it("should add and reject pending requests", async () => {
     const request = { request: reqData.generateMockRequest(1, "foo", ["bar"]), internalID: 1 };
-    const prom = transportReqMan.addRequest(request, undefined);
+    const prom = transportReqMan.addRequest(request, null);
     transportReqMan.settlePendingRequest([request], new Error("rejecting"));
     await expect(prom).rejects.toThrowError("rejecting");
   });
@@ -97,7 +97,7 @@ describe("Transport Request Manager", () => {
     const prom = transportReqMan.addRequest({
       request: reqData.generateMockRequest(1, "foo", ["bar"]),
       internalID: 1,
-    }, undefined);
+    }, null);
 
     // Verify that the response resolves the pending request and the response event fires
     transportReqMan.transportEventChannel.on("response", async (responseData) => {
@@ -126,7 +126,7 @@ describe("Transport Request Manager", () => {
     // tslint:disable-next-line:no-empty
     const reject = () => {
     };
-    const prom = transportReqMan.addRequest([{ request: requestData, resolve, reject }], undefined);
+    const prom = transportReqMan.addRequest([{ request: requestData, resolve, reject }], null);
 
     // Verify that the response resolves the pending request and the response event fires
     transportReqMan.transportEventChannel.on("response", (responseData) => {
@@ -154,7 +154,7 @@ describe("Transport Request Manager", () => {
     // tslint:disable-next-line:no-empty
     const reject = () => { };
 
-    transportReqMan.addRequest([{ request: requestData, resolve, reject }], undefined);
+    transportReqMan.addRequest([{ request: requestData, resolve, reject }], null);
 
     // Resolve pending request;
     const err = transportReqMan.resolveResponse(JSON.stringify([res]), false) as Error;
@@ -180,7 +180,7 @@ describe("Transport Request Manager", () => {
     const prom = transportReqMan.addRequest({
       request: reqData.generateMockRequest(1, "foo", ["bar"]),
       internalID: 1,
-    }, undefined);
+    }, null);
     transportReqMan.transportEventChannel.on("response", async (data) => {
       if (data.error === undefined) {
         throw new Error("Missing error");
diff --git a/src/transports/TransportRequestManager.ts b/src/transports/TransportRequestManager.ts
index 3a097ff..ff9d6b7 100644
--- a/src/transports/TransportRequestManager.ts
+++ b/src/transports/TransportRequestManager.ts
@@ -23,7 +23,7 @@ export class TransportRequestManager {
     this.pendingBatchRequest = {};
     this.transportEventChannel = new EventEmitter();
   }
-  public addRequest(data: JSONRPCRequestData, timeout: number | undefined): Promise<any> {
+  public addRequest(data: JSONRPCRequestData, timeout: number | null): Promise<any> {
     this.transportEventChannel.emit("pending", data);
     if (data instanceof Array) {
       this.addBatchReq(data, timeout);
@@ -67,7 +67,7 @@ export class TransportRequestManager {
     }
   }
 
-  private addBatchReq(batches: IBatchRequest[], timeout: number | undefined) {
+  private addBatchReq(batches: IBatchRequest[], timeout: number | null) {
     batches.forEach((batch) => {
       const { resolve, reject } = batch;
       const { internalID } = batch.request;
@@ -76,9 +76,9 @@ export class TransportRequestManager {
     });
     return Promise.resolve();
   }
-  private addReq(id: string | number, timeout?: number) {
+  private addReq(id: string | number, timeout: number | null) {
     return new Promise((resolve, reject) => {
-      if (timeout) {
+      if (timeout !== null && timeout) {
         this.setRequestTimeout(id, timeout, reject);
       }
       this.pendingRequest[id] = { resolve, reject };
diff --git a/src/transports/WebSocketTransport.ts b/src/transports/WebSocketTransport.ts
index 4139b94..9c38d79 100644
--- a/src/transports/WebSocketTransport.ts
+++ b/src/transports/WebSocketTransport.ts
@@ -26,7 +26,7 @@ class WebSocketTransport extends Transport {
     });
   }
 
-  public async sendData(data: JSONRPCRequestData, timeout: number | undefined = 5000): Promise<any> {
+  public async sendData(data: JSONRPCRequestData, timeout: number | null = 5000): Promise<any> {
     let prom = this.transportRequestManager.addRequest(data, timeout);
     const notifications = getNotifications(data);
     this.connection.send(JSON.stringify(this.parseData(data)), (err?: Error) => {