diff --git a/h/models/user.py b/h/models/user.py
index f2bfc35230d..3391f3f1ea4 100644
--- a/h/models/user.py
+++ b/h/models/user.py
@@ -166,7 +166,7 @@ def __table_args__(cls):  # pylint:disable=no-self-argument
         sa.Text(),
         default=partial(generate, USER_PUBID_LENGTH),
         unique=True,
-        nullable=True,
+        nullable=False,
     )
 
     #: Username as chosen by the user on registration