diff --git a/core/admin/mailu/ui/forms.py b/core/admin/mailu/ui/forms.py
index 4f7a30ae..57c106c3 100644
--- a/core/admin/mailu/ui/forms.py
+++ b/core/admin/mailu/ui/forms.py
@@ -90,9 +90,10 @@ class UserSignupForm(flask_wtf.FlaskForm):
     localpart = fields.StringField(_('Email address'), [validators.DataRequired(), validators.Regexp(LOCALPART_REGEX)])
     pw = fields.PasswordField(_('Password'), [validators.DataRequired()])
     pw2 = fields.PasswordField(_('Confirm password'), [validators.EqualTo('pw')])
-    captcha = flask_wtf.RecaptchaField()
     submit = fields.SubmitField(_('Sign up'))
 
+class UserSignupFormCaptcha(UserSignupForm):
+    captcha = flask_wtf.RecaptchaField()
 
 class UserSettingsForm(flask_wtf.FlaskForm):
     displayed_name = fields.StringField(_('Displayed name'))
diff --git a/core/admin/mailu/ui/views/users.py b/core/admin/mailu/ui/views/users.py
index c54d22ec..f7f75c32 100644
--- a/core/admin/mailu/ui/views/users.py
+++ b/core/admin/mailu/ui/views/users.py
@@ -170,7 +170,11 @@ def user_signup(domain_name=None):
             available_domains=available_domains)
     domain = available_domains.get(domain_name) or flask.abort(404)
     quota_bytes = domain.max_quota_bytes or app.config['DEFAULT_QUOTA']
-    form = forms.UserSignupForm()
+    if app.config['RECAPTCHA_PUBLIC_KEY'] == "" or app.config['RECAPTCHA_PRIVATE_KEY'] == "":
+        form = forms.UserSignupForm()
+    else:
+        form = forms.UserSignupFormCaptcha()
+
     if form.validate_on_submit():
         if domain.has_email(form.localpart.data):
             flask.flash('Email is already used', 'error')