diff --git a/src/index.ts b/src/index.ts
index 43d7b5a..c98e81d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -93,7 +93,7 @@ export interface ClientOptions {
    * Note that request timeouts are retried by default, so in a worst-case scenario you may wait
    * much longer than this timeout before the promise succeeds or fails.
    */
-  timeout?: number;
+  timeout?: number | undefined;
 
   /**
    * An HTTP agent used to manage HTTP(S) connections.
@@ -101,7 +101,7 @@ export interface ClientOptions {
    * If not provided, an agent will be constructed by default in the Node.js environment,
    * otherwise no agent is used.
    */
-  httpAgent?: Agent;
+  httpAgent?: Agent | undefined;
 
   /**
    * Specify a custom `fetch` function implementation.
@@ -117,7 +117,7 @@ export interface ClientOptions {
    *
    * @default 2
    */
-  maxRetries?: number;
+  maxRetries?: number | undefined;
 
   /**
    * Default headers to include with every request to the API.
@@ -125,7 +125,7 @@ export interface ClientOptions {
    * These can be removed in individual requests by explicitly setting the
    * header to `undefined` or `null` in request options.
    */
-  defaultHeaders?: Core.Headers;
+  defaultHeaders?: Core.Headers | undefined;
 
   /**
    * Default query parameters to include with every request to the API.
@@ -133,7 +133,7 @@ export interface ClientOptions {
    * These can be removed in individual requests by explicitly setting the
    * param to `undefined` in request options.
    */
-  defaultQuery?: Core.DefaultQuery;
+  defaultQuery?: Core.DefaultQuery | undefined;
 }
 
 /**