diff --git a/package-lock.json b/package-lock.json
index 65fdb4a..ea09bc5 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "jepub",
-  "version": "2.1.0",
+  "version": "2.1.1",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index e3b8ef7..abababe 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "jepub",
-  "version": "2.1.0",
+  "version": "2.1.1",
   "description": "Generate simple EPUB books with JavaScript.",
   "main": "src/jepub.js",
   "scripts": {
diff --git a/src/jepub.js b/src/jepub.js
index eea4728..cab3d40 100644
--- a/src/jepub.js
+++ b/src/jepub.js
@@ -101,8 +101,10 @@ export default class jEpub {
             ext = utils.mime2ext(mime);
         } else if (data instanceof ArrayBuffer) {
             ext = imageType(new Uint8Array(data));
-            mime = ext.mime;
-            if (ext) ext = utils.mime2ext(mime);
+            if (ext) {
+                mime = ext.mime;
+                ext = utils.mime2ext(mime);
+            }
         } else {
             throw 'Cover data is not valid';
         }