diff --git a/src/posts/attachments.js b/src/posts/attachments.js
index 679247da27..3683aa0de4 100644
--- a/src/posts/attachments.js
+++ b/src/posts/attachments.js
@@ -2,6 +2,7 @@
 
 const crypto = require('crypto');
 const _ = require('lodash');
+const mime = require('mime');
 
 const db = require('../database');
 
@@ -50,6 +51,11 @@ Attachments.update = async (pid, attachments) => {
 			_type = 'attachment';
 		}
 
+		if (!mediaType) { // MIME type guessing
+			const { pathname } = new URL(url);
+			mediaType = mime.getType(pathname);
+		}
+
 		bulkOps.hash.push([key, { _type, mediaType, url, name, width, height }]);
 		hashes.push(hash);
 	});