diff --git a/slapos/onetimeupload/__init__.py b/slapos/onetimeupload/__init__.py
index cd97177c5b84d14796e31af0c67108aa7d4f4448..94bc44f5a586b8c02bcf33f67050c1022c684ec7 100644
--- a/slapos/onetimeupload/__init__.py
+++ b/slapos/onetimeupload/__init__.py
@@ -76,6 +76,10 @@ class Config:
     self.key = key
 
 def run(config):
+  """
+  Will accept to upload a file only once. When a file has been uploaded,
+  it will refuse any other upload.
+  """
 
   app = Flask(__name__)