diff --git a/telebot/apihelper.py b/telebot/apihelper.py
index 5ea37c4fd..3044b226d 100644
--- a/telebot/apihelper.py
+++ b/telebot/apihelper.py
@@ -2271,6 +2271,12 @@ def convert_input_media_array(array):
             if media_dict['media'].startswith('attach://'):
                 key = media_dict['media'].replace('attach://', '')
                 files[key] = input_media.media
+            if 'thumbnail' in media_dict:
+                thumbnail = media_dict['thumbnail']
+                if isinstance(thumbnail, types.InputFile):
+                    thumbnail_key = 'thumbnail_' + key  
+                    files[thumbnail_key] = thumbnail    
+                    media_dict['thumbnail'] = 'attach://' + thumbnail_key                           
             media.append(media_dict)
     return json.dumps(media), files
 
diff --git a/telebot/asyncio_helper.py b/telebot/asyncio_helper.py
index 56604c750..d11245d56 100644
--- a/telebot/asyncio_helper.py
+++ b/telebot/asyncio_helper.py
@@ -2243,6 +2243,12 @@ async def convert_input_media_array(array):
             if media_dict['media'].startswith('attach://'):
                 key = media_dict['media'].replace('attach://', '')
                 files[key] = input_media.media
+            if 'thumbnail' in media_dict:
+                thumbnail = media_dict['thumbnail']
+                if isinstance(thumbnail, types.InputFile):
+                    thumbnail_key = 'thumbnail_' + key  
+                    files[thumbnail_key] = thumbnail    
+                    media_dict['thumbnail'] = 'attach://' + thumbnail_key                    
             media.append(media_dict)
     return json.dumps(media), files