diff --git a/telethon/utils.py b/telethon/utils.py
index 3afa9b6b..8da7e0ec 100644
--- a/telethon/utils.py
+++ b/telethon/utils.py
@@ -1550,5 +1550,7 @@ def _photo_size_byte_count(size):
         return len(size.bytes)
     elif isinstance(size, types.PhotoSizeEmpty):
         return 0
+    elif isinstance(size, types.PhotoSizeProgressive):
+        return max(size.sizes)
     else:
         return None