diff --git a/HISTORY.md b/HISTORY.md
index d567753..5cb6800 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -7,6 +7,8 @@ https://github.com/josdejong/jsoneditor
 
 - Fixed broken link to the Ace editor website (https://ace.c9.io/).
   Thanks @p3x-robot.
+- Fix #1027: create IE11 Array polyfills `find` and `findIndex` in such a way 
+  that they are not iterable.
 
 
 ## 2020-05-24, version 9.0.0
diff --git a/src/js/polyfills.js b/src/js/polyfills.js
index 0c59ac2..8c42bd1 100644
--- a/src/js/polyfills.js
+++ b/src/js/polyfills.js
@@ -25,24 +25,32 @@ if (typeof Element !== 'undefined') {
 // simple polyfill for Array.findIndex
 if (!Array.prototype.findIndex) {
   // eslint-disable-next-line no-extend-native
-  Array.prototype.findIndex = function (predicate) {
-    for (let i = 0; i < this.length; i++) {
-      const element = this[i]
-      if (predicate.call(this, element, i, this)) {
-        return i
+  Object.defineProperty(Array.prototype, 'findIndex', {
+    value: function (predicate) {
+      for (let i = 0; i < this.length; i++) {
+        const element = this[i]
+        if (predicate.call(this, element, i, this)) {
+          return i
+        }
       }
-    }
-    return -1
-  }
+      return -1
+    },
+    configurable: true,
+    writable: true
+  })
 }
 
 // Polyfill for Array.find
 if (!Array.prototype.find) {
   // eslint-disable-next-line no-extend-native
-  Array.prototype.find = function (predicate) {
-    const i = this.findIndex(predicate)
-    return this[i]
-  }
+  Object.defineProperty(Array.prototype, 'find', {
+    value: function (predicate) {
+      const i = this.findIndex(predicate)
+      return this[i]
+    },
+    configurable: true,
+    writable: true
+  })
 }
 
 // Polyfill for String.trim