diff --git a/twoot.py b/twoot.py
index af9d454..eaf6833 100755
--- a/twoot.py
+++ b/twoot.py
@@ -314,9 +314,15 @@ def main(argv):
             # Download picture
             media = requests.get(photo)
 
+            # Fix to avoid media_post failing because mime_type is NoneType
+            # "Can only concatenate str to str"
+            mime_type = media.headers.get('content-type')
+            if type(mime_type) is None:
+                mime_type = ""
+
             # Upload picture to Mastodon instance
             try:
-                media_posted = mastodon.media_post(media.content, mime_type=media.headers.get('content-type'))
+                media_posted = mastodon.media_post(media.content, mime_type)
                 media_ids.append(media_posted['id'])
             except MastodonAPIError:  # Media cannot be uploaded (invalid format, dead link, etc.)
                 pass