diff --git a/src/export/packer/packer.spec.ts b/src/export/packer/packer.spec.ts
index 110089da01..b61165ab46 100644
--- a/src/export/packer/packer.spec.ts
+++ b/src/export/packer/packer.spec.ts
@@ -46,4 +46,24 @@ describe("Packer", () => {
             });
         });
     });
+
+    describe("#toBase64String()", () => {
+        it("should create a standard docx file", async function() {
+            this.timeout(99999999);
+            const str = await packer.toBase64String(file);
+
+            assert.isDefined(str);
+            assert.isTrue(str.length > 0);
+        });
+
+        it("should handle exception if it throws any", () => {
+            // tslint:disable-next-line:no-any
+            const compiler = stub((packer as any).compiler, "compile");
+
+            compiler.throwsException();
+            return packer.toBase64String(file).catch((error) => {
+                assert.isDefined(error);
+            });
+        });
+    });
 });
diff --git a/src/export/packer/packer.ts b/src/export/packer/packer.ts
index e85b42c8ea..856f74b59e 100644
--- a/src/export/packer/packer.ts
+++ b/src/export/packer/packer.ts
@@ -10,21 +10,30 @@ export class Packer {
 
     public async toBuffer(file: File): Promise<Buffer> {
         const zip = await this.compiler.compile(file);
-        const zipData = (await zip.generateAsync({ type: "nodebuffer" })) as Buffer;
+        const zipData = (await zip.generateAsync({
+            type: "nodebuffer",
+            mimeType: "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+        })) as Buffer;
 
         return zipData;
     }
 
     public async toBase64String(file: File): Promise<string> {
         const zip = await this.compiler.compile(file);
-        const zipData = (await zip.generateAsync({ type: "base64" })) as string;
+        const zipData = (await zip.generateAsync({
+            type: "base64",
+            mimeType: "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+        })) as string;
 
         return zipData;
     }
 
     public async toBlob(file: File): Promise<Blob> {
         const zip = await this.compiler.compile(file);
-        const zipData = (await zip.generateAsync({ type: "blob" })) as Blob;
+        const zipData = (await zip.generateAsync({
+            type: "blob",
+            mimeType: "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+        })) as Blob;
 
         return zipData;
     }