diff --git a/youtube_dl/postprocessor/embedthumbnail.py b/youtube_dl/postprocessor/embedthumbnail.py
index 56be914b8f..acb7958c97 100644
--- a/youtube_dl/postprocessor/embedthumbnail.py
+++ b/youtube_dl/postprocessor/embedthumbnail.py
@@ -50,6 +50,19 @@ def run(self, info):
 
             self.run_ffmpeg_multiple_files([filename, thumbnail_filename], temp_filename, options)
 
+            if not self._already_have_thumbnail:
+                os.remove(encodeFilename(thumbnail_filename))
+            os.remove(encodeFilename(filename))
+            os.rename(encodeFilename(temp_filename), encodeFilename(filename))
+
+		if info['ext'] == 'mkv':
+			options = [
+				'-c', 'copy', '-attach', thumbnail_filename, '-metadata:s:t', 'mimetype=image/jpeg']
+			
+            self._downloader.to_screen('[ffmpeg] Adding thumbnail to "%s"' % filename)
+
+            self.run_ffmpeg_multiple_files([filename], temp_filename, options)
+
             if not self._already_have_thumbnail:
                 os.remove(encodeFilename(thumbnail_filename))
             os.remove(encodeFilename(filename))