diff --git a/demo/demo5.js b/demo/demo5.js
index 604ddcd0e5..2b2ed42511 100644
--- a/demo/demo5.js
+++ b/demo/demo5.js
@@ -6,6 +6,7 @@ var paragraph = new docx.Paragraph("Hello World");
 doc.addParagraph(paragraph);
 
 const image = doc.createImage("./demo/images/image1.jpeg");
+const image2 = doc.createImage("./demo/images/dog.png");
 
 var exporter = new docx.LocalPacker(doc);
 exporter.pack('My Document');
diff --git a/demo/images/dog.png b/demo/images/dog.png
new file mode 100644
index 0000000000..2791b64087
Binary files /dev/null and b/demo/images/dog.png differ
diff --git a/src/file/media/media.ts b/src/file/media/media.ts
index b77ebf76fd..b683e5a3d8 100644
--- a/src/file/media/media.ts
+++ b/src/file/media/media.ts
@@ -26,7 +26,7 @@ export class Media {
         const dimensions = sizeOf(filePath);
 
         const imageData = {
-            referenceId: this.map.values.length + 3,
+            referenceId: this.map.size + 3,
             stream: fs.createReadStream(filePath),
             path: filePath,
             fileName: key,
diff --git a/template/[Content_Types].xml b/template/[Content_Types].xml
index 6d07a1a165..365a95edb6 100644
--- a/template/[Content_Types].xml
+++ b/template/[Content_Types].xml
@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
     <Types xmlns="http://schemas.openxmlformats.org/package/2006/content-types">
+        <Default Extension="png" ContentType="image/png"/>
         <Default Extension="jpeg" ContentType="image/jpeg"/>
         <Default Extension="rels" ContentType="application/vnd.openxmlformats-package.relationships+xml" />
         <Default Extension="xml" ContentType="application/xml" />