diff --git a/lib/internal/test_runner/reporter/tap.js b/lib/internal/test_runner/reporter/tap.js
index b345d18fc667a3..cd0bbe8ca53003 100644
--- a/lib/internal/test_runner/reporter/tap.js
+++ b/lib/internal/test_runner/reporter/tap.js
@@ -224,6 +224,9 @@ function jsToYaml(indent, name, value, seen) {
     }
 
     if (errIsAssertion) {
+      // Note that we're deliberately creating shallow copies of the `seen`
+      // set here in order to isolate the discovery of circular references
+      // within the expected and actual properties respectively.
       result += jsToYaml(indent, 'expected', errExpected, new SafeSet(seen));
       result += jsToYaml(indent, 'actual', errActual, new SafeSet(seen));
       if (errOperator) {