diff --git a/app/validators/unreserved_username_validator.rb b/app/validators/unreserved_username_validator.rb
index c2311a89a..634ceb06e 100644
--- a/app/validators/unreserved_username_validator.rb
+++ b/app/validators/unreserved_username_validator.rb
@@ -2,20 +2,22 @@
 
 class UnreservedUsernameValidator < ActiveModel::Validator
   def validate(account)
-    return if account.username.nil?
-    account.errors.add(:username, I18n.t('accounts.reserved_username')) if reserved_username?(account.username)
+    @username = account.username
+    return if @username.nil?
+
+    account.errors.add(:username, I18n.t('accounts.reserved_username')) if reserved_username?
   end
 
   private
 
-  def pam_controlled?(value)
+  def pam_controlled?
     return false unless Devise.pam_authentication && Devise.pam_controlled_service
-    Rpam2.account(Devise.pam_controlled_service, value).present?
+    Rpam2.account(Devise.pam_controlled_service, @username).present?
   end
 
-  def reserved_username?(value)
-    return true if pam_controlled?(value)
+  def reserved_username?
+    return true if pam_controlled?
     return false unless Setting.reserved_usernames
-    Setting.reserved_usernames.include?(value.downcase)
+    Setting.reserved_usernames.include?(@username.downcase)
   end
 end
diff --git a/spec/validators/unreserved_username_validator_spec.rb b/spec/validators/unreserved_username_validator_spec.rb
new file mode 100644
index 000000000..0187941b0
--- /dev/null
+++ b/spec/validators/unreserved_username_validator_spec.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe UnreservedUsernameValidator, type: :validator do
+  describe '#validate' do
+    before do
+      allow(validator).to receive(:reserved_username?) { reserved_username }
+      validator.validate(account)
+    end
+
+    let(:validator) { described_class.new }
+    let(:account)   { double(username: username, errors: errors) }
+    let(:errors )   { double(add: nil) }
+
+    context '@username.nil?' do
+      let(:username)  { nil }
+
+      it 'not calls errors.add' do
+        expect(errors).not_to have_received(:add).with(:username, any_args)
+      end
+    end
+
+    context '!@username.nil?' do
+      let(:username)  { '' }
+
+      context 'reserved_username?' do
+        let(:reserved_username) { true }
+
+        it 'calls erros.add' do
+          expect(errors).to have_received(:add).with(:username, I18n.t('accounts.reserved_username'))
+        end
+      end
+
+      context '!reserved_username?' do
+        let(:reserved_username) { false }
+
+        it 'not calls erros.add' do
+          expect(errors).not_to have_received(:add).with(:username, any_args)
+        end
+      end
+    end
+  end
+end