diff --git a/chrome/content/zotero/xpcom/mime.js b/chrome/content/zotero/xpcom/mime.js
index a89f167d4..ca1d50dcf 100644
--- a/chrome/content/zotero/xpcom/mime.js
+++ b/chrome/content/zotero/xpcom/mime.js
@@ -330,8 +330,6 @@ Zotero.MIME = new function(){
 				var mimeType = xmlhttp.channel.contentType;
 			}
 			
-			if(!mimeType) mimeType = 'application/octet-stream';	//unknown item type according to RFC 2046 section 4.5.1
-			
 			var nsIURL = Components.classes["@mozilla.org/network/standard-url;1"]
 						.createInstance(Components.interfaces.nsIURL);
 			nsIURL.spec = url;
diff --git a/chrome/content/zotero/xpcom/translation/translate_item.js b/chrome/content/zotero/xpcom/translation/translate_item.js
index e64d7e405..54df7d162 100644
--- a/chrome/content/zotero/xpcom/translation/translate_item.js
+++ b/chrome/content/zotero/xpcom/translation/translate_item.js
@@ -405,12 +405,12 @@ Zotero.Translate.ItemSaver.prototype = {
 				// Save attachment if snapshot pref enabled or not HTML
 				// (in which case downloadAssociatedFiles applies)
 				} else {
-					if(!attachment.mimeType && attachment.mimeType !== '') {	//in case '' indicates unknwon mime type at some point
+					if(!attachment.mimeType && attachment.mimeType !== '') {
 						Zotero.debug("Translate: No mimeType specified for a possible snapshot. Trying to determine mimeType.", 4);
 						var me = this;
 						try {
 							Zotero.MIME.getMIMETypeFromURL(attachment.url, function (mimeType, hasNativeHandler) {
-								attachment.mimeType = mimeType;
+								attachment.mimeType = mimeType || '';
 								me._saveAttachmentDownload(attachment, parentID, attachmentCallback);
 							}, this._cookieSandbox);
 						} catch(e) {