diff --git a/app/models/ci/runner_namespace.rb b/app/models/ci/runner_namespace.rb
index 3269f86e8ca..420e34df091 100644
--- a/app/models/ci/runner_namespace.rb
+++ b/app/models/ci/runner_namespace.rb
@@ -2,7 +2,7 @@ module Ci
   class RunnerNamespace < ActiveRecord::Base
     extend Gitlab::Ci::Model
 
-    belongs_to :runner
+    belongs_to :runner, validate: true
     belongs_to :namespace, class_name: '::Namespace'
     belongs_to :group, class_name: '::Group', foreign_key: :namespace_id
   end
diff --git a/spec/models/ci/runner_spec.rb b/spec/models/ci/runner_spec.rb
index 4dc990350d2..51d5e666cd6 100644
--- a/spec/models/ci/runner_spec.rb
+++ b/spec/models/ci/runner_spec.rb
@@ -66,6 +66,13 @@ describe Ci::Runner do
         expect(instance_runner).not_to be_valid
         expect(instance_runner.errors.full_messages).to include('Runner cannot assign project to a non-project runner')
       end
+
+      it 'should fail to save a group assigned to a project runner even if the runner is already saved' do
+        group_runner
+
+        expect { create(:group, runners: [project_runner]) }
+          .to raise_error(ActiveRecord::RecordInvalid)
+      end
     end
   end