diff --git a/docs/primer.md b/docs/primer.md
index aecc368b..2ffbf53b 100644
--- a/docs/primer.md
+++ b/docs/primer.md
@@ -274,6 +274,7 @@ First, define a fixture class. By convention, you should give it the name
 class QueueTest : public ::testing::Test {
  protected:
   void SetUp() override {
+     // q0_ remains empty
      q1_.Enqueue(1);
      q2_.Enqueue(2);
      q2_.Enqueue(3);