diff --git a/index.d.ts b/index.d.ts
index 9887119bed..27dbd1a479 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -122,6 +122,10 @@ export interface ParamEncoder {
   (value: any, defaultEncoder: (value: any) => any): any;
 }
 
+export interface CustomParamsSerializer {
+  (params: Record<string, any>, options?: ParamsSerializerOptions): string;
+}
+
 export interface ParamsSerializerOptions extends SerializerOptions {
   encode?: ParamEncoder;
 }
@@ -134,7 +138,7 @@ export interface AxiosRequestConfig<D = any> {
   transformResponse?: AxiosResponseTransformer | AxiosResponseTransformer[];
   headers?: AxiosRequestHeaders;
   params?: any;
-  paramsSerializer?: ParamsSerializerOptions;
+  paramsSerializer?: ParamsSerializerOptions | CustomParamsSerializer;
   data?: D;
   timeout?: number;
   timeoutErrorMessage?: string;
diff --git a/lib/core/Axios.js b/lib/core/Axios.js
index ef7e810129..b9ea3e3a2b 100644
--- a/lib/core/Axios.js
+++ b/lib/core/Axios.js
@@ -59,6 +59,10 @@ Axios.prototype.request = function request(configOrUrl, config) {
     }, false);
   }
 
+  var paramsSerializer = config.paramsSerializer;
+
+  utils.isFunction(paramsSerializer) && (config.paramsSerializer = {serialize: paramsSerializer});
+
   // filter out skipped interceptors
   var requestInterceptorChain = [];
   var synchronousRequestInterceptors = true;