diff --git a/lib/reporters/base.js b/lib/reporters/base.js
index 0754fe1a37..44c0d7a5fa 100644
--- a/lib/reporters/base.js
+++ b/lib/reporters/base.js
@@ -466,7 +466,7 @@ function stringify(obj) {
  function canonicalize(obj, stack) {
    stack = stack || [];
 
-   if (utils.indexOf(stack, obj) !== -1) return obj;
+   if (utils.indexOf(stack, obj) !== -1) return '[Circular]';
 
    var canonicalizedObj;
 
diff --git a/mocha.js b/mocha.js
index 19edc87d97..66943316f1 100644
--- a/mocha.js
+++ b/mocha.js
@@ -2317,7 +2317,7 @@ function stringify(obj) {
  function canonicalize(obj, stack) {
    stack = stack || [];
 
-   if (utils.indexOf(stack, obj) !== -1) return obj;
+   if (utils.indexOf(stack, obj) !== -1) return '[Circular]';
 
    var canonicalizedObj;