diff --git a/chrome/content/zotero/bindings/attachmentbox.xml b/chrome/content/zotero/bindings/attachmentbox.xml
index 0630c6fd8e..2c75f6affc 100644
--- a/chrome/content/zotero/bindings/attachmentbox.xml
+++ b/chrome/content/zotero/bindings/attachmentbox.xml
@@ -388,15 +388,21 @@
 						
 						// Rename associated file
 						if (checkState.value) {
-							var renamed = item.renameAttachmentFile(newTitle.value);
+							var newFilename = newTitle.value.trim();
+							if (newFilename.search(/\.\w{1,10}$/) == -1) {
+								// User did not specify extension. Use current
+								var oldExt = item.getFilename().match(/\.\w{1,10}$/);
+								if (oldExt) newFilename += oldExt[0];
+							}
+							var renamed = item.renameAttachmentFile(newFilename);
 							if (renamed == -1) {
 								var confirmed = nsIPS.confirm(
 									window,
 									'',
-									newTitle.value + ' exists. Overwrite existing file?'
+									newFilename + ' exists. Overwrite existing file?'
 								);
 								if (confirmed) {
-									item.renameAttachmentFile(newTitle.value, true);
+									item.renameAttachmentFile(newFilename, true);
 									break;
 								}
 								// If they said not to overwrite existing file,