diff --git a/app/controllers/hyku/invitations_controller.rb b/app/controllers/hyku/invitations_controller.rb
index dbe246cd..2aa11fca 100644
--- a/app/controllers/hyku/invitations_controller.rb
+++ b/app/controllers/hyku/invitations_controller.rb
@@ -14,6 +14,7 @@ def create
       authorize! :grant_admin_role, User if params[:user][:role] == ::RolesService::ADMIN_ROLE
       self.resource = User.find_by(email: params[:user][:email]) || invite_resource
 
+      resource.add_default_group_membership!
       resource.add_role(params[:user][:role], Site.instance) if params[:user][:role].present?
 
       yield resource if block_given?
diff --git a/spec/controllers/hyku/invitations_controller_spec.rb b/spec/controllers/hyku/invitations_controller_spec.rb
index 4ed0cf5c..bf87c4ff 100644
--- a/spec/controllers/hyku/invitations_controller_spec.rb
+++ b/spec/controllers/hyku/invitations_controller_spec.rb
@@ -31,5 +31,31 @@
       expect(response).to redirect_to Hyrax::Engine.routes.url_helpers.admin_users_path(locale: 'en')
       expect(flash[:notice]).to eq 'An invitation email has been sent to user@guest.org.'
     end
+
+    context 'when user already exists' do
+      let(:user) { create(:user) }
+
+      # Mimic the state of a user who is only active in other tenants;
+      # i.e. a user who has no roles in this tenant
+      before do
+        user.roles.destroy_all
+      end
+
+      it 'adds the user to the registered group' do
+        expect(user.roles).to be_empty
+        expect(user.groups).to be_empty
+
+        post :create, params: {
+          user: {
+            email: user.email,
+            role: ''
+          }
+        }
+
+        user.reload
+        expect(user.roles).not_to be_empty
+        expect(user.groups).to eq([Ability.registered_group_name])
+      end
+    end
   end
 end