diff --git a/telegram/document.py b/telegram/document.py
index 14cc1efdb..364a3f983 100644
--- a/telegram/document.py
+++ b/telegram/document.py
@@ -32,8 +32,9 @@ class Document(TelegramObject):
                         file_size=data.get('file_size', None))
 
     def to_dict(self):
-        data = {'file_id': self.file_id,
-                'thumb': self.thumb.to_dict()}
+        data = {'file_id': self.file_id}
+        if self.thumb:
+            data['thumb'] = self.thumb.to_dict()
         if self.file_name:
             data['file_name'] = self.file_name
         if self.mime_type:
diff --git a/telegram/video.py b/telegram/video.py
index e4690631c..b21c400a2 100644
--- a/telegram/video.py
+++ b/telegram/video.py
@@ -44,8 +44,9 @@ class Video(TelegramObject):
         data = {'file_id': self.file_id,
                 'width': self.width,
                 'height': self.height,
-                'duration': self.duration,
-                'thumb': self.thumb.to_dict()}
+                'duration': self.duration}
+        if self.thumb:
+            data['thumb'] = self.thumb.to_dict()
         if self.mime_type:
             data['mime_type'] = self.mime_type
         if self.file_size: