diff --git a/src/jsonData.js b/src/jsonData.js
index d1343f7..73912c0 100644
--- a/src/jsonData.js
+++ b/src/jsonData.js
@@ -3,10 +3,9 @@
  * All functions are pure and don't mutate the JSONData.
  */
 
-import { isObject } from './utils/objectUtils'
 import { setIn, updateIn, getIn, deleteIn } from './utils/immutabilityHelpers'
 import { compareAsc, compareDesc } from './utils/arrayUtils'
-import { stringConvert } from  './utils/typeUtils'
+import { isObject, stringConvert } from  './utils/typeUtils'
 import { findUniqueName } from  './utils/stringUtils'
 import isEqual from 'lodash/isEqual'
 import cloneDeep from 'lodash/isEqual'
diff --git a/src/typedef.js b/src/typedef.js
index 116bbe1..2a5f164 100644
--- a/src/typedef.js
+++ b/src/typedef.js
@@ -17,7 +17,7 @@
  *   value: *?
  * }} ValueData
  *
- * @typedef {Array.<string | number>} Path
+ * @typedef {Array.<string>} Path
  *
  * @typedef {ObjectData | ArrayData | ValueData} JSONData
  *
diff --git a/src/utils/immutabilityHelpers.js b/src/utils/immutabilityHelpers.js
index ce6091d..e8eea5e 100644
--- a/src/utils/immutabilityHelpers.js
+++ b/src/utils/immutabilityHelpers.js
@@ -1,6 +1,7 @@
 'use strict';
 
-import { isObject, clone } from  './objectUtils'
+import clone from 'lodash/clone'
+import { isObjectOrArray } from  './typeUtils'
 
 /**
  * Immutability helpers
@@ -26,7 +27,7 @@ export function getIn (object, path) {
   let i = 0
 
   while(i < path.length) {
-    if (Array.isArray(value) || isObject(value)) {
+    if (isObjectOrArray(value)) {
       value = value[path[i]]
     }
     else {
@@ -53,17 +54,20 @@ export function setIn (object, path, value) {
     return value
   }
 
-  const key = path[0]
-  const updated = cloneOrCreate(key, object)
+  if (!isObjectOrArray(object)) {
+    throw new Error('Path does not exist')
+  }
 
-  const updatedValue = setIn(updated[key], path.slice(1), value)
-  if (updated[key] === updatedValue) {
+  const key = path[0]
+  const updatedValue = setIn(object[key], path.slice(1), value)
+  if (object[key] === updatedValue) {
     // return original object unchanged when the new value is identical to the old one
     return object
   }
   else {
-    updated[key] = updatedValue
-    return updated
+    const updatedObject = clone(object)
+    updatedObject[key] = updatedValue
+    return updatedObject
   }
 }
 /**
@@ -80,17 +84,20 @@ export function updateIn (object, path, callback) {
     return callback(object)
   }
 
-  const key = path[0]
-  const updated = cloneOrCreate(key, object)
+  if (!isObjectOrArray(object)) {
+    throw new Error('Path doesn\'t exist')
+  }
 
+  const key = path[0]
   const updatedValue = updateIn(object[key], path.slice(1), callback)
-  if (updated[key] === updatedValue) {
+  if (object[key] === updatedValue) {
     // return original object unchanged when the new value is identical to the old one
     return object
   }
   else {
-    updated[key] = updatedValue
-    return updated
+    const updatedObject = clone(object)
+    updatedObject[key] = updatedValue
+    return updatedObject
   }
 }
 
@@ -107,48 +114,39 @@ export function deleteIn (object, path) {
     return object
   }
 
+  if (!isObjectOrArray(object)) {
+    return object
+  }
+
   if (path.length === 1) {
     const key = path[0]
-    const updated = clone(object)
-    if (Array.isArray(updated)) {
-      updated.splice(key, 1)
+    if (object[key] === undefined) {
+      // key doesn't exist. return object unchanged
+      return object
     }
     else {
-      delete updated[key]
-    }
+      const updatedObject = clone(object)
 
-    return updated
+      if (Array.isArray(updatedObject)) {
+        updatedObject.splice(key, 1)
+      }
+      else {
+        delete updatedObject[key]
+      }
+
+      return updatedObject
+    }
   }
 
   const key = path[0]
-  const child = object[key]
-  if (Array.isArray(child) || isObject(child)) {
-    const updated = clone(object)
-    updated[key] = deleteIn(child, path.slice(1))
-    return updated
-  }
-  else {
-    // child property doesn't exist. just do nothing
+  const updatedValue = deleteIn(object[key], path.slice(1))
+  if (object[key] === updatedValue) {
+    // object is unchanged
     return object
   }
-}
-
-/**
- * Helper function to clone an array or object, or to create a new object
- * when `object` is undefined. When object is anything else, the function will
- * throw an error
- * @param {string | number} key
- * @param {Object | Array | undefined} object
- * @return {Array | Object}
- */
-function cloneOrCreate (key, object) {
-  if (object === undefined) {
-    return (typeof key === 'number') ? [] : {} // create new object or array
+  else {
+    const updatedObject = clone(object)
+    updatedObject[key] = updatedValue
+    return updatedObject
   }
-
-  if (typeof object === 'object' || Array.isArray(object)) {
-    return clone(object)
-  }
-
-  throw new Error('Cannot override existing property ' + JSON.stringify(object))
 }
diff --git a/src/utils/objectUtils.js b/src/utils/objectUtils.js
deleted file mode 100644
index 467b55f..0000000
--- a/src/utils/objectUtils.js
+++ /dev/null
@@ -1,67 +0,0 @@
-
-// TODO: unit test isObject
-
-/**
- * Test whether a value is an object (and not an Array or Date or primitive value)
- *
- * @param {*} value
- * @return {boolean}
- */
-export function isObject (value) {
-  return typeof value === 'object' &&
-      value !== null &&
-      !Array.isArray(value) &&
-      value.toString() === '[object Object]'
-}
-
-// TODO: unit test clone
-
-/**
- * Flat clone the properties of an object or array
- * @param {Object | Array} value
- * @return {Object | Array} Returns a flat clone of the object or Array
- */
-export function clone (value) {
-  if (Array.isArray(value)) {
-    return value.slice(0)
-  }
-  else if (isObject(value)) {
-    const cloned = {}
-
-    Object.keys(value).forEach(key => {
-      cloned[key] = value[key]
-    })
-
-    return cloned
-  }
-  else {
-    // a primitive value
-    return value
-  }
-}
-
-// TODO: test cloneDeep
-
-/**
- * Deep clone the properties of an object or array
- * @param {Object | Array} value
- * @return {Object | Array} Returns a deep clone of the object or Array
- */
-export function cloneDeep (value) {
-  if (Array.isArray(value)) {
-    return value.map(cloneDeep)
-  }
-  else if (isObject(value)) {
-    const cloned = {}
-
-    Object.keys(value).forEach(key => {
-      cloned[key] = cloneDeep(value[key])
-    })
-
-    return cloned
-  }
-  else {
-    // a primitive value
-    return value
-  }
-}
diff --git a/src/utils/typeUtils.js b/src/utils/typeUtils.js
index f8bdac7..0534d89 100644
--- a/src/utils/typeUtils.js
+++ b/src/utils/typeUtils.js
@@ -1,4 +1,28 @@
 
+// TODO: unit test isObject
+
+/**
+ * Test whether a value is an Object (and not an Array!)
+ *
+ * @param {*} value
+ * @return {boolean}
+ */
+export function isObject (value) {
+  return typeof value === 'object' &&
+      value !== null &&
+      !Array.isArray(value)
+}
+
+/**
+ * Test whether a value is an Object or an Array
+ *
+ * @param {*} value
+ * @return {boolean}
+ */
+export function isObjectOrArray (value) {
+  return typeof value === 'object' && value !== null
+}
+
 /**
  * Get the type of a value
  * @param {*} value
diff --git a/test/immutabilityHelpers.test.js b/test/immutabilityHelpers.test.js
index 2362215..8d026ed 100644
--- a/test/immutabilityHelpers.test.js
+++ b/test/immutabilityHelpers.test.js
@@ -20,8 +20,8 @@ test('getIn', t => {
   }
 
   t.deepEqual(getIn(obj, ['a', 'b']), {c: 2})
-  t.is(getIn(obj, ['e', 1, 'f']), 5)
-  t.is(getIn(obj, ['e', 999, 'f']), undefined)
+  t.is(getIn(obj, ['e', '1', 'f']), 5)
+  t.is(getIn(obj, ['e', '999', 'f']), undefined)
   t.is(getIn(obj, ['non', 'existing', 'path']), undefined)
 })
 
@@ -61,15 +61,7 @@ test('setIn basic', t => {
 test('setIn non existing path', t => {
   const obj = {}
 
-  const updated = setIn(obj, ['a', 'b', 'c'], 4)
-
-  t.deepEqual (updated, {
-    a: {
-      b: {
-        c: 4
-      }
-    }
-  })
+  t.throws(() => setIn(obj, ['a', 'b', 'c'], 4), /Path does not exist/)
 })
 
 test('setIn replace value with object should throw an exception', t => {
@@ -78,9 +70,7 @@ test('setIn replace value with object should throw an exception', t => {
     d: 3
   }
 
-  t.throws(function () {
-    const updated = setIn(obj, ['a', 'b', 'c'], 4)
-  }, /Cannot override existing property/)
+  t.throws(()  => setIn(obj, ['a', 'b', 'c'], 4), /Path does not exist/)
 })
 
 test('setIn replace value inside nested array', t => {
@@ -96,7 +86,7 @@ test('setIn replace value inside nested array', t => {
     d: 5
   }
 
-  const updated = setIn(obj, ['a', 2, 'c'], 8)
+  const updated = setIn(obj, ['a', '2', 'c'], 8)
 
   t.deepEqual (updated, {
     a: [
@@ -254,7 +244,7 @@ test('deleteIn array', t => {
     e: 5
   }
 
-  const updated = deleteIn(obj, ['a', 'b', 1, 'c'])
+  const updated = deleteIn(obj, ['a', 'b', '1', 'c'])
   t.deepEqual (updated, {
     a: {
       b: [1, {d: 3} , 4]
@@ -271,4 +261,11 @@ test('deleteIn array', t => {
   })
 
   t.truthy (obj !== updated)
+})
+
+test('deleteIn non existing path', t => {
+  const obj = { a: {}}
+
+  const updated = deleteIn(obj, ['a', 'b'])
+  t.truthy (updated === obj)
 })
\ No newline at end of file