diff --git a/types/index.d.ts b/types/index.d.ts
index 3c2bfe7..c0a951d 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -110,7 +110,7 @@ export interface DateNFOption {
 /** Options for read and readFile */
 export interface ParsingOptions extends CommonOptions {
     /** Input data encoding */
-    type?: 'base64' | 'binary' | 'buffer' | 'file' | 'array';
+    type?: 'base64' | 'binary' | 'buffer' | 'file' | 'array' | 'string';
 
     /** Default codepage */
     codepage?: number;
@@ -193,7 +193,7 @@ export interface ParsingOptions extends CommonOptions {
 /** Options for write and writeFile */
 export interface WritingOptions extends CommonOptions {
     /** Output data encoding */
-    type?: 'base64' | 'binary' | 'buffer' | 'file' | 'array';
+    type?: 'base64' | 'binary' | 'buffer' | 'file' | 'array' | 'string';
 
     /**
      * Generate Shared String Table
diff --git a/types/xlsx-tests.ts b/types/xlsx-tests.ts
index 4681e33..9dfa100 100644
--- a/types/xlsx-tests.ts
+++ b/types/xlsx-tests.ts
@@ -50,6 +50,13 @@ XLSX.utils.book_append_sheet(newwb, aoa2, "AOA");
 XLSX.utils.book_append_sheet(newwb, js2ws, "JSON");
 const bstrxlsx: string = XLSX.write(newwb, {type: "binary", bookType: "xlsx" });
 
+const wb_1: XLSX.WorkBook = XLSX.read(XLSX.write(newwb, {type: "base64", bookType: "xlsx" }), {type: "base64"});
+const wb_2: XLSX.WorkBook = XLSX.read(XLSX.write(newwb, {type: "binary", bookType: "xlsx" }), {type: "binary"});
+const wb_3: XLSX.WorkBook = XLSX.read(XLSX.write(newwb, {type: "buffer", bookType: "xlsx" }), {type: "buffer"});
+const wb_4: XLSX.WorkBook = XLSX.read(XLSX.write(newwb, {type: "file", bookType: "xlsx" }), {type: "file"});
+const wb_5: XLSX.WorkBook = XLSX.read(XLSX.write(newwb, {type: "array", bookType: "xlsx" }), {type: "array"});
+const wb_6: XLSX.WorkBook = XLSX.read(XLSX.write(newwb, {type: "string", bookType: "xlsx" }), {type: "string"});
+
 const CFB = XLSX.CFB;
 const vbawb = XLSX.readFile("test.xlsm", {bookVBA:true});
 if(vbawb.vbaraw) {