diff --git a/xmlrpc/index.d.ts b/xmlrpc/index.d.ts
index b962be4324..8425d4672c 100644
--- a/xmlrpc/index.d.ts
+++ b/xmlrpc/index.d.ts
@@ -84,6 +84,13 @@ declare module 'xmlrpc' {
             decodeIso8601(time: string): Date;
             encodeIso8601(date: Date): string;
         }
+
+        export class CustomType {
+            tagName: string;
+            raw: string;
+            constructor(raw: string);
+            serialize(xml: any): any; // XMLElementOrXMLNode declared by xmlbuilder
+        }
     }
 
     export = xmlrpc;
diff --git a/xmlrpc/xmlrpc-tests.ts b/xmlrpc/xmlrpc-tests.ts
index a7e8dcffbe..b9cdff2e3f 100644
--- a/xmlrpc/xmlrpc-tests.ts
+++ b/xmlrpc/xmlrpc-tests.ts
@@ -23,4 +23,14 @@ const server = xmlrpc.createServer(serverOpts, () => {
     client.methodCall('hello', ['world'], (err, val) => {
         console.log(val);
     });
+
+    class Value extends xmlrpc.CustomType {
+        constructor(value: any) {
+            super(value);
+            this.tagName = 'Value';
+        }
+    }
+    client.methodCall('hello', [new Value('custom_string_value')], (err, val) => {
+        console.log(val);
+    });
 });