diff --git a/benchmark/circles-fixture.js b/benchmark/circles-fixture.js
new file mode 100644
index 0000000..f4456db
--- /dev/null
+++ b/benchmark/circles-fixture.js
@@ -0,0 +1,64 @@
+'use strict'
+
+function buildPeopleGraph () {
+  const people = []
+
+  function createPerson (name, age) {
+    return {
+      name,
+      age,
+      friends: [],
+      parents: [],
+      children: []
+    }
+  }
+
+  // Populate the array with people
+  people.push(createPerson('John', 50))
+  people.push(createPerson('Jane', 48))
+  people.push(createPerson('Mike', 28))
+  people.push(createPerson('Sara', 26))
+  people.push(createPerson('Tom', 30))
+  people.push(createPerson('Lily', 27))
+  people.push(createPerson('Emily', 5))
+  people.push(createPerson('Jack', 3))
+  people.push(createPerson('Alice', 65))
+  people.push(createPerson('Bob', 66))
+
+  // Define relationships
+
+  // John and Jane are parents of Mike and Sara
+  people[0].children.push(people[2], people[3]) // John's children
+  people[1].children.push(people[2], people[3]) // Jane's children
+  people[2].parents.push(people[0], people[1]) // Mike's parents
+  people[3].parents.push(people[0], people[1]) // Sara's parents
+
+  // Tom and Lily are parents of Emily and Jack
+  people[4].children.push(people[6], people[7]) // Tom's children
+  people[5].children.push(people[6], people[7]) // Lily's children
+  people[6].parents.push(people[4], people[5]) // Emily's parents
+  people[7].parents.push(people[4], people[5]) // Jack's parents
+
+  // Alice and Bob are John's and Jane's parents (grandparents)
+  people[0].parents.push(people[8], people[9]) // John's parents
+  people[1].parents.push(people[8], people[9]) // Jane's parents
+  people[8].children.push(people[0], people[1]) // Alice's children
+  people[9].children.push(people[0], people[1]) // Bob's children
+
+  // Add friends relationships (mutual circular relationships)
+  people[2].friends.push(people[4]) // Mike and Tom are friends
+  people[4].friends.push(people[2])
+
+  people[3].friends.push(people[5]) // Sara and Lily are friends
+  people[5].friends.push(people[3])
+
+  people[0].friends.push(people[9]) // John and Bob (his father) are friends
+  people[9].friends.push(people[0])
+
+  people[1].friends.push(people[8]) // Jane and Alice (her mother) are friends
+  people[8].friends.push(people[1])
+
+  return people
+}
+
+module.exports = buildPeopleGraph()
diff --git a/benchmark/circles.js b/benchmark/circles.js
new file mode 100644
index 0000000..1c9c353
--- /dev/null
+++ b/benchmark/circles.js
@@ -0,0 +1,61 @@
+'use strict'
+
+/* global structuredClone */
+
+const bench = require('fastbench')
+const lodashCloneDeep = require('lodash.clonedeep')
+const fastCopy = require('fast-copy').default
+const obj = require('./circles-fixture')
+const clone = require('..')
+const nanoCopy = require('nano-copy')
+const ramdaClone = require('ramda').clone
+const cloneCircles = clone({ circles: true })
+const cloneCirclesProto = clone({ circles: true, proto: true })
+const max = 1000
+
+const run = bench([
+  function benchLodashCloneDeep (cb) {
+    for (let i = 0; i < max; i++) {
+      lodashCloneDeep(obj)
+    }
+    setImmediate(cb)
+  },
+  function benchFastCopy (cb) {
+    for (let i = 0; i < max; i++) {
+      fastCopy(obj)
+    }
+    setImmediate(cb)
+  },
+  function benchNanoCopy (cb) {
+    for (let i = 0; i < max; i++) {
+      nanoCopy(obj)
+    }
+    setImmediate(cb)
+  },
+  function benchRamdaClone (cb) {
+    for (let i = 0; i < max; i++) {
+      ramdaClone(obj)
+    }
+    setImmediate(cb)
+  },
+  function benchRfdcCircles (cb) {
+    for (let i = 0; i < max; i++) {
+      cloneCircles(obj)
+    }
+    setImmediate(cb)
+  },
+  function benchRfdcCirclesProto (cb) {
+    for (let i = 0; i < max; i++) {
+      cloneCirclesProto(obj)
+    }
+    setImmediate(cb)
+  },
+  function benchStructuredClone (cb) {
+    for (let i = 0; i < max; i++) {
+      structuredClone(obj)
+    }
+    setImmediate(cb)
+  }
+], 100)
+
+run(run)
diff --git a/index.js b/index.js
index a964561..2d28752 100644
--- a/index.js
+++ b/index.js
@@ -93,13 +93,10 @@ function rfdc (opts) {
 }
 
 function rfdcCircles (opts) {
-  const refs = []
-  const refsNew = []
-
   const constructorHandlers = new Map()
   constructorHandlers.set(Date, (o) => new Date(o))
-  constructorHandlers.set(Map, (o, fn) => new Map(cloneArray(Array.from(o), fn)))
-  constructorHandlers.set(Set, (o, fn) => new Set(cloneArray(Array.from(o), fn)))
+  constructorHandlers.set(Map, (o, refs, fn) => new Map(cloneArray(Array.from(o), refs, fn)))
+  constructorHandlers.set(Set, (o, refs, fn) => new Set(cloneArray(Array.from(o), refs, fn)))
   if (opts.constructorHandlers) {
     for (const handler of opts.constructorHandlers) {
       constructorHandlers.set(handler[0], handler[1])
@@ -109,7 +106,7 @@ function rfdcCircles (opts) {
   let handler = null
   return opts.proto ? cloneProto : clone
 
-  function cloneArray (a, fn) {
+  function cloneArray (a, refs, fn) {
     const keys = Object.keys(a)
     const a2 = new Array(keys.length)
     for (let i = 0; i < keys.length; i++) {
@@ -117,82 +114,91 @@ function rfdcCircles (opts) {
       const cur = a[k]
       if (typeof cur !== 'object' || cur === null) {
         a2[k] = cur
-      } else if (cur.constructor !== Object && (handler = constructorHandlers.get(cur.constructor))) {
-        a2[k] = handler(cur, fn)
-      } else if (ArrayBuffer.isView(cur)) {
-        a2[k] = copyBuffer(cur)
       } else {
-        const index = refs.indexOf(cur)
-        if (index !== -1) {
-          a2[k] = refsNew[index]
+        const ref = refs.get(cur)
+        if (ref !== undefined) {
+          a2[k] = ref
         } else {
-          a2[k] = fn(cur)
+          let cur2
+          if (cur.constructor !== Object && (handler = constructorHandlers.get(cur.constructor))) {
+            cur2 = handler(cur, refs, fn)
+          } else if (ArrayBuffer.isView(cur)) {
+            cur2 = copyBuffer(cur)
+          } else {
+            cur2 = fn(cur, refs)
+          }
+          refs.set(cur, cur2)
+          a2[k] = cur2
         }
       }
     }
     return a2
   }
 
-  function clone (o) {
+  function clone (o, refs = new Map()) {
     if (typeof o !== 'object' || o === null) return o
-    if (Array.isArray(o)) return cloneArray(o, clone)
+    if (Array.isArray(o)) return cloneArray(o, refs, clone)
     if (o.constructor !== Object && (handler = constructorHandlers.get(o.constructor))) {
-      return handler(o, clone)
+      return handler(o, refs, clone)
     }
     const o2 = {}
-    refs.push(o)
-    refsNew.push(o2)
+    refs.set(o, o2)
     for (const k in o) {
       if (Object.hasOwnProperty.call(o, k) === false) continue
       const cur = o[k]
       if (typeof cur !== 'object' || cur === null) {
         o2[k] = cur
-      } else if (cur.constructor !== Object && (handler = constructorHandlers.get(cur.constructor))) {
-        o2[k] = handler(cur, clone)
-      } else if (ArrayBuffer.isView(cur)) {
-        o2[k] = copyBuffer(cur)
       } else {
-        const i = refs.indexOf(cur)
-        if (i !== -1) {
-          o2[k] = refsNew[i]
+        const ref = refs.get(cur)
+        if (ref !== undefined) {
+          o2[k] = ref
         } else {
-          o2[k] = clone(cur)
+          let cur2
+          if (cur.constructor !== Object && (handler = constructorHandlers.get(cur.constructor))) {
+            cur2 = handler(cur, refs, clone)
+          } else if (ArrayBuffer.isView(cur)) {
+            cur2 = copyBuffer(cur)
+          } else {
+            cur2 = clone(cur, refs)
+          }
+          refs.set(cur, cur2)
+          o2[k] = cur2
         }
       }
     }
-    refs.pop()
-    refsNew.pop()
     return o2
   }
 
-  function cloneProto (o) {
+  function cloneProto (o, refs = new Map()) {
     if (typeof o !== 'object' || o === null) return o
-    if (Array.isArray(o)) return cloneArray(o, cloneProto)
+    if (Array.isArray(o)) return cloneArray(o, refs, cloneProto)
     if (o.constructor !== Object && (handler = constructorHandlers.get(o.constructor))) {
-      return handler(o, cloneProto)
+      return handler(o, refs, cloneProto)
     }
     const o2 = {}
-    refs.push(o)
-    refsNew.push(o2)
+    refs.set(o, o2)
     for (const k in o) {
       const cur = o[k]
       if (typeof cur !== 'object' || cur === null) {
         o2[k] = cur
-      } else if (cur.constructor !== Object && (handler = constructorHandlers.get(cur.constructor))) {
-        o2[k] = handler(cur, cloneProto)
-      } else if (ArrayBuffer.isView(cur)) {
-        o2[k] = copyBuffer(cur)
       } else {
-        const i = refs.indexOf(cur)
-        if (i !== -1) {
-          o2[k] = refsNew[i]
+        const ref = refs.get(cur)
+        if (ref !== undefined) {
+          o2[k] = ref
         } else {
-          o2[k] = cloneProto(cur)
+          let cur2
+          if (cur.constructor !== Object && (handler = constructorHandlers.get(cur.constructor))) {
+            cur2 = handler(cur, refs, cloneProto)
+          } else if (ArrayBuffer.isView(cur)) {
+            cur2 = copyBuffer(cur)
+          } else {
+            cur2 = cloneProto(cur, refs)
+          }
+          refs.set(cur, cur2)
+          o2[k] = cur2
         }
       }
     }
-    refs.pop()
-    refsNew.pop()
     return o2
   }
 }
diff --git a/test/index.js b/test/index.js
index 5bdd9ac..da27e6f 100644
--- a/test/index.js
+++ b/test/index.js
@@ -120,6 +120,27 @@ test('custom constructor handler', async ({ same, ok, isNot }) => {
   same(cloned.foo.s, data.foo.s, 'same values')
   isNot(cloned.foo, data.foo, 'different objects')
 })
+test('custom constructor handler - circular objects', async ({ same, ok, is, isNot }) => {
+  class Foo {
+    constructor (s) {
+      this.s = s
+    }
+  }
+  const a = { foo: new Foo('foo1') }
+  const b = { foo: new Foo('foo2') }
+  a.other = b
+  b.other = a
+  const data = { a, b }
+  const cloned = rfdc({ circles: true, constructorHandlers: [[Foo, (o) => new Foo(o.s)]] })(data)
+  ok(cloned.a.foo instanceof Foo)
+  ok(cloned.b.foo instanceof Foo)
+  same(cloned.a.foo.s, data.a.foo.s, 'same values')
+  same(cloned.b.foo.s, data.b.foo.s, 'same values')
+  isNot(cloned.a.foo, data.a.foo, 'different objects')
+  isNot(cloned.b.foo, data.b.foo, 'different objects')
+  is(cloned.a.other, cloned.b, 'same objects')
+  is(cloned.b.other, cloned.a, 'same objects')
+})
 test('custom RegExp handler', async ({ same, ok, isNot }) => {
   const data = { regex: /foo/ }
   const cloned = rfdc({ constructorHandlers: [[RegExp, (o) => new RegExp(o)]] })(data)