diff --git a/types/json2csv/JSON2CSVBase.d.ts b/types/json2csv/JSON2CSVBase.d.ts
index 022c7cab77..51c87e1a6c 100644
--- a/types/json2csv/JSON2CSVBase.d.ts
+++ b/types/json2csv/JSON2CSVBase.d.ts
@@ -27,6 +27,7 @@ export declare namespace json2csv {
         unwind?: string | Array<string>;
         unwindBlank?: boolean;
         flatten?: boolean;
+        flattenSeparator?: string;
         defaultValue?: string;
         quote?: string;
         doubleQuote?: string;
diff --git a/types/json2csv/index.d.ts b/types/json2csv/index.d.ts
index edf693cc3d..a8e734576b 100644
--- a/types/json2csv/index.d.ts
+++ b/types/json2csv/index.d.ts
@@ -2,6 +2,7 @@
 // Project: https://github.com/zemirco/json2csv
 // Definitions by: Juanjo Diaz <https://github.com/juanjoDiaz>
 //                 Daniel Gooß <https://github.com/dangoo>
+//                 Denis Yilmaz <https://github.com/denisyilmaz>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 // TypeScript Version: 2.2
 
diff --git a/types/json2csv/json2csv-tests.ts b/types/json2csv/json2csv-tests.ts
index cad3745d68..179a0df127 100644
--- a/types/json2csv/json2csv-tests.ts
+++ b/types/json2csv/json2csv-tests.ts
@@ -86,6 +86,15 @@ try {
     console.error(err);
 }
 
+// Test for Synchronous Parser with flatten and custom flattenSeparator
+try {
+    const parser = new Parser<any>({ ...opts, flatten: true, flattenSeparator: ' / ' });
+    const csv = parser.parse({ car: '', price: 1, foo: { bar: '' } });
+    console.log(csv);
+} catch (err) {
+    console.error(err);
+}
+
 // Test convenience method "parse"
 try {
     const csv = parse(data, opts);