diff --git a/youtube_dl/postprocessor/ffmpeg.py b/youtube_dl/postprocessor/ffmpeg.py
index 22d7ac65a..6daa6a8b4 100644
--- a/youtube_dl/postprocessor/ffmpeg.py
+++ b/youtube_dl/postprocessor/ffmpeg.py
@@ -508,6 +508,7 @@ class FFmpegSubtitlesConvertorPP(FFmpegPostProcessor):
 
                 with io.open(srt_file, 'wt', encoding='utf-8') as f:
                     f.write(srt_data)
+                old_file = srt_file
 
                 ext = 'srt'
                 subs[lang] = {