diff --git a/spec/services/compare_service_spec.rb b/spec/services/compare_service_spec.rb
index 0e4ef69ec19..fadd43635a6 100644
--- a/spec/services/compare_service_spec.rb
+++ b/spec/services/compare_service_spec.rb
@@ -19,5 +19,18 @@ describe CompareService do
 
       it { expect(subject.diffs.size).to eq(3) }
     end
+
+    context 'compare with target branch that does not exist' do
+      subject { service.execute(project, 'non-existent-ref') }
+
+      it { expect(subject).to be_nil }
+    end
+
+    context 'compare with source branch that does not exist' do
+      let(:service) { described_class.new(project, 'non-existent-branch') }
+      subject { service.execute(project, 'non-existent-ref') }
+
+      it { expect(subject).to be_nil }
+    end
   end
 end