diff --git a/lib/detectify/query_builder/base.rb b/lib/detectify/query_builder/base.rb
index 466042f..6563ff4 100644
--- a/lib/detectify/query_builder/base.rb
+++ b/lib/detectify/query_builder/base.rb
@@ -4,8 +4,8 @@ class Base
       attr_reader :domain, :subdomain
 
       def initialize(domain, subdomain)
-        @domain    = domain
-        @subdomain = subdomain
+        @domain    = domain.downcase if domain.is_a?(String)
+        @subdomain = subdomain.downcase if subdomain.is_a?(String)
       end
 
       def build
diff --git a/spec/detectify/query_builder/base_spec.rb b/spec/detectify/query_builder/base_spec.rb
new file mode 100644
index 0000000..de2755f
--- /dev/null
+++ b/spec/detectify/query_builder/base_spec.rb
@@ -0,0 +1,17 @@
+require 'spec_helper'
+
+RSpec.describe Detectify::QueryBuilder::Base do
+  let(:domain) { 'DOMAIN' }
+  let(:subdomain) { 'SUBDOMAIN' }
+  subject { Detectify::QueryBuilder::Base.new(domain, subdomain) }
+
+  describe '#initialize' do
+    it 'sets domain in downcase' do
+      expect(subject.domain).to eq(domain.downcase)
+    end
+
+    it 'sets subdomain in downcase' do
+      expect(subject.subdomain).to eq(subdomain.downcase)
+    end
+  end
+end