diff --git a/index.d.ts b/index.d.ts
index 27dbd1a479..85bf706131 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -123,7 +123,7 @@ export interface ParamEncoder {
 }
 
 export interface CustomParamsSerializer {
-  (params: Record<string, any>, options?: ParamsSerializerOptions): string;
+  (params: object, options?: ParamsSerializerOptions): string;
 }
 
 export interface ParamsSerializerOptions extends SerializerOptions {
diff --git a/lib/core/Axios.js b/lib/core/Axios.js
index b9ea3e3a2b..84410891ac 100644
--- a/lib/core/Axios.js
+++ b/lib/core/Axios.js
@@ -61,6 +61,13 @@ Axios.prototype.request = function request(configOrUrl, config) {
 
   var paramsSerializer = config.paramsSerializer;
 
+  if (paramsSerializer !== undefined) {
+    validator.assertOptions(paramsSerializer, {
+      encode: validators.function,
+      serialize: validators.function
+    }, true);
+  }
+
   utils.isFunction(paramsSerializer) && (config.paramsSerializer = {serialize: paramsSerializer});
 
   // filter out skipped interceptors
diff --git a/lib/helpers/buildURL.js b/lib/helpers/buildURL.js
index bebacb3aee..1d9bce98ab 100644
--- a/lib/helpers/buildURL.js
+++ b/lib/helpers/buildURL.js
@@ -35,12 +35,20 @@ module.exports = function buildURL(url, params, options) {
 
   var _encode = options && options.encode || encode;
 
-  var serializerParams = utils.isURLSearchParams(params) ?
-    params.toString() :
-    new AxiosURLSearchParams(params, options).toString(_encode);
+  var serializeFn = options && options.serialize;
 
-  if (serializerParams) {
-    url += (url.indexOf('?') === -1 ? '?' : '&') + serializerParams;
+  let serializedParams;
+
+  if (serializeFn) {
+    serializedParams = serializeFn(params, options);
+  } else {
+    serializedParams = utils.isURLSearchParams(params) ?
+      params.toString() :
+      new AxiosURLSearchParams(params, options).toString(_encode);
+  }
+
+  if (serializedParams) {
+    url += (url.indexOf('?') === -1 ? '?' : '&') + serializedParams;
   }
 
   return url;
diff --git a/test/specs/helpers/buildURL.spec.js b/test/specs/helpers/buildURL.spec.js
index 0bee3e9a05..6239c2430f 100644
--- a/test/specs/helpers/buildURL.spec.js
+++ b/test/specs/helpers/buildURL.spec.js
@@ -63,4 +63,20 @@ describe('helpers::buildURL', function () {
   it('should support URLSearchParams', function () {
     expect(buildURL('/foo', new URLSearchParams('bar=baz'))).toEqual('/foo?bar=baz');
   });
+
+  it('should support custom serialize function', function () {
+    const params = {
+      x: 1
+    }
+
+    const options = {
+      serialize: (thisParams, thisOptions) => {
+        expect(thisParams).toEqual(params);
+        expect(thisOptions).toEqual(options);
+        return "rendered"
+      }
+    };
+
+    expect(buildURL('/foo', params, options)).toEqual('/foo?rendered');
+  });
 });
diff --git a/test/typescript/axios.ts b/test/typescript/axios.ts
index 2bfb23c07a..60873d89a3 100644
--- a/test/typescript/axios.ts
+++ b/test/typescript/axios.ts
@@ -22,7 +22,8 @@ const config: AxiosRequestConfig = {
   params: { id: 12345 },
   paramsSerializer: {
     indexes: true,
-    encode: (value) => value
+    encode: (value) => value,
+    serialize: (value, options) => String(value)
   },
   data: { foo: 'bar' },
   timeout: 10000,