diff --git a/lenticular_cloud/form/auth.py b/lenticular_cloud/form/auth.py
index 064e90c..54b2c19 100644
--- a/lenticular_cloud/form/auth.py
+++ b/lenticular_cloud/form/auth.py
@@ -30,7 +30,7 @@ class ConsentForm(FlaskForm):
 class RegistrationForm(FlaskForm):
     username = StringField(gettext('Username'), validators=[
         DataRequired(),
-        Regexp('^[a-zA-Z0-9-.]+$', message=gettext('Only `a-z`, `A-Z`, `0-9`, `-.` is allowed for username'))
+        Regexp('^[a-z0-9-.]+$', message=gettext('Only `a-z`, `0-9`, `-.` is allowed for username'))
         ])
     password = PasswordField(gettext('Password'), validators=[
         DataRequired(),