diff --git a/youtube_dl/extractor/tudou.py b/youtube_dl/extractor/tudou.py
index 7a3891b89..96e0732bd 100644
--- a/youtube_dl/extractor/tudou.py
+++ b/youtube_dl/extractor/tudou.py
@@ -57,7 +57,8 @@ class TudouIE(InfoExtractor):
         segments = json.loads(segs_json)
         # It looks like the keys are the arguments that have to be passed as
         # the hd field in the request url, we pick the higher
-        quality = sorted(segments.keys())[-1]
+        # Also, filter non-number qualities (see issue #3643).
+        quality = sorted(filter(lambda k: k.isdigit(), segments.keys()))[-1]
         parts = segments[quality]
         result = []
         len_parts = len(parts)