diff --git a/lib/ci/api/entities.rb b/lib/ci/api/entities.rb
index 66c05773b68..e00d91a6b45 100644
--- a/lib/ci/api/entities.rb
+++ b/lib/ci/api/entities.rb
@@ -50,6 +50,10 @@ module Ci
 
         expose :variables
         expose :depends_on_builds, using: Build
+
+        expose :registry_url, if: ->(_, _) { Gitlab.config.registry.enabled } do |_|
+          Gitlab.config.registry.host_port
+        end
       end
 
       class Runner < Grape::Entity
diff --git a/spec/requests/ci/api/builds_spec.rb b/spec/requests/ci/api/builds_spec.rb
index 6d49c42c215..bd4d3d61714 100644
--- a/spec/requests/ci/api/builds_spec.rb
+++ b/spec/requests/ci/api/builds_spec.rb
@@ -17,6 +17,10 @@ describe Ci::API::API do
       let!(:build) { create(:ci_build, pipeline: pipeline, name: 'spinach', stage: 'test', stage_idx: 0) }
       let(:user_agent) { 'gitlab-ci-multi-runner 1.5.2 (1-5-stable; go1.6.3; linux/amd64)' }
 
+      before do
+        stub_container_registry_config(enabled: false)
+      end
+
       shared_examples 'no builds available' do
         context 'when runner sends version in User-Agent' do
           context 'for stable version' do
@@ -53,6 +57,31 @@ describe Ci::API::API do
         it 'updates runner info' do
           expect { register_builds }.to change { runner.reload.contacted_at }
         end
+
+        context 'when registry is enabled' do
+          before do
+            stub_container_registry_config(enabled: true, host_port: 'registry.example.com:5005')
+          end
+
+          it 'sends registry_url key' do
+            register_builds info: { platform: :darwin }
+
+            expect(json_response).to have_key('registry_url')
+            expect(json_response['registry_url']).to eq("registry.example.com:5005")
+          end
+        end
+
+        context 'when registry is disabled' do
+          before do
+            stub_container_registry_config(enabled: false, host_port: 'registry.example.com:5005')
+          end
+
+          it 'does not send registry_url key' do
+            register_builds info: { platform: :darwin }
+
+            expect(json_response).not_to have_key('registry_url')
+          end
+        end
       end
 
       context 'when builds are finished' do