diff --git a/youtube_dl/compat.py b/youtube_dl/compat.py
index 8b4d0287c..9e506352f 100644
--- a/youtube_dl/compat.py
+++ b/youtube_dl/compat.py
@@ -98,6 +98,9 @@ except ImportError:
         append = res.append
 
         for item in bits[1:]:
+            if item == '':
+                append(b'%')
+                continue
             try:
                 append(item[:2].decode('hex'))
                 append(item[2:])