diff --git a/telethon/utils.py b/telethon/utils.py
index ad2d2e1c..05cf9432 100644
--- a/telethon/utils.py
+++ b/telethon/utils.py
@@ -634,7 +634,7 @@ def get_input_location(location):
             id=location.id,
             access_hash=location.access_hash,
             file_reference=location.file_reference,
-            thumb_size=''  # Presumably to download one of its thumbnails
+            thumb_size=location.sizes[-1].type
         ))
 
     if isinstance(location, types.FileLocationToBeDeprecated):
diff --git a/telethon_generator/data/errors.csv b/telethon_generator/data/errors.csv
index 649a6d65..7ef1b0da 100644
--- a/telethon_generator/data/errors.csv
+++ b/telethon_generator/data/errors.csv
@@ -141,7 +141,7 @@ MESSAGE_TOO_LONG,400,Message was too long. Current maximum length is 4096 UTF-8
 MSG_WAIT_FAILED,400,A waiting call returned an error
 MT_SEND_QUEUE_TOO_LONG,500,
 NEED_CHAT_INVALID,500,The provided chat is invalid
-NEED_MEMBER_INVALID,500,The provided member is invalid
+NEED_MEMBER_INVALID,500,The provided member is invalid or does not exist (for example a thumb size)
 NETWORK_MIGRATE_X,303,The source IP address is associated with DC {new_dc}
 NEW_SALT_INVALID,400,The new salt is invalid
 NEW_SETTINGS_INVALID,400,The new settings are invalid