diff --git a/config/jest.setup.js b/config/jest.setup.js
index 5f93791..0166051 100644
--- a/config/jest.setup.js
+++ b/config/jest.setup.js
@@ -2,6 +2,7 @@ import '@testing-library/jest-dom/extend-expect'
 import FDBFactory from 'fake-indexeddb/build/FDBFactory'
 import FDBKeyRange from 'fake-indexeddb/build/FDBKeyRange'
 import { Crypto } from '@peculiar/webcrypto'
+import { ResizeObserver } from 'd2l-resize-aware/resize-observer-module.js'
 
 jest.mock('node-fetch', () => require('fetch-mock-jest').sandbox())
 jest.setTimeout(60000)
@@ -9,6 +10,7 @@ jest.setTimeout(60000)
 global.fetch = require('node-fetch')
 global.Response = fetch.Response
 global.crypto = new Crypto()
+global.ResizeObserver = ResizeObserver
 
 process.env.NODE_ENV = 'test'
 
diff --git a/jest.config.cjs b/jest.config.cjs
index 8203699..82f8563 100644
--- a/jest.config.cjs
+++ b/jest.config.cjs
@@ -15,7 +15,7 @@ module.exports = {
   },
   moduleFileExtensions: ['js', 'svelte'],
   testPathIgnorePatterns: ['node_modules'],
-  transformIgnorePatterns: ['<rootDir>/node_modules/(?!lodash-es|if-emoji)'],
+  transformIgnorePatterns: ['<rootDir>/node_modules/(?!lodash-es|if-emoji|d2l-resize-aware)'],
   bail: true,
   verbose: true,
   silent: false,
diff --git a/package.json b/package.json
index d268e17..b9cd8c6 100644
--- a/package.json
+++ b/package.json
@@ -81,6 +81,7 @@
     "compression": "^1.7.4",
     "conventional-changelog-cli": "^2.1.1",
     "cssnano": "^4.1.10",
+    "d2l-resize-aware": "BrightspaceUI/resize-aware#semver:^1.2.2",
     "emoji-picker-element-data": "^1.0.0",
     "emojibase-data": "^5.1.1",
     "express": "^4.17.1",
diff --git a/src/picker/components/Picker/Picker.js b/src/picker/components/Picker/Picker.js
index 8598b36..4266bad 100644
--- a/src/picker/components/Picker/Picker.js
+++ b/src/picker/components/Picker/Picker.js
@@ -20,7 +20,7 @@ import {
 } from '../../constants'
 import { uniqBy } from '../../../shared/uniqBy'
 import { summarizeEmojisForUI } from '../../utils/summarizeEmojisForUI'
-import { calculateWidth, resizeObserverSupported } from '../../utils/calculateWidth'
+import * as widthCalculator from '../../utils/widthCalculator'
 import { checkZwjSupport } from '../../utils/checkZwjSupport'
 import { requestPostAnimationFrame } from '../../utils/requestPostAnimationFrame'
 import { stop } from '../../../shared/marks'
@@ -253,7 +253,7 @@ $: {
 
 // eslint-disable-next-line no-unused-vars
 function calculateEmojiGridWidth (node) {
-  return calculateWidth(node, width => {
+  return widthCalculator.calculateWidth(node, width => {
     /* istanbul ignore next */
     const newNumColumns = process.env.NODE_ENV === 'test'
       ? DEFAULT_NUM_COLUMNS
@@ -280,7 +280,7 @@ $: currentGroup = groups[currentGroupIndex]
 
 // eslint-disable-next-line no-unused-vars
 function calculateIndicatorWidth (node) {
-  return calculateWidth(node, width => {
+  return widthCalculator.calculateWidth(node, width => {
     computedIndicatorWidth = width
   })
 }
@@ -290,14 +290,12 @@ function calculateIndicatorWidth (node) {
 // So we calculate of the indicator and use exact pixel values in the animation instead
 // (where ResizeObserver is supported).
 $: {
-  /* istanbul ignore if */
-  if (resizeObserverSupported) {
-    // eslint-disable-next-line no-unused-vars
-    indicatorStyle = `transform: translateX(${currentGroupIndex * computedIndicatorWidth}px);` // exact pixels
-  } else {
-    // eslint-disable-next-line no-unused-vars
-    indicatorStyle = `transform: translateX(${currentGroupIndex * 100}%);`// fallback to percent-based
-  }
+  // eslint-disable-next-line no-unused-vars
+  indicatorStyle = `transform: translateX(${
+    widthCalculator.resizeObserverSupported
+      ? `${currentGroupIndex * computedIndicatorWidth}px` // exact pixels
+      : `${currentGroupIndex * 100}%` // fallback to percent-based
+  })`
 }
 
 //
diff --git a/src/picker/utils/calculateWidth.js b/src/picker/utils/widthCalculator.js
similarity index 77%
rename from src/picker/utils/calculateWidth.js
rename to src/picker/utils/widthCalculator.js
index ae6cf4f..9d5089d 100644
--- a/src/picker/utils/calculateWidth.js
+++ b/src/picker/utils/widthCalculator.js
@@ -4,11 +4,15 @@
 
 import { requestAnimationFrame } from './requestAnimationFrame'
 
-export const resizeObserverSupported = typeof ResizeObserver === 'function'
+export let resizeObserverSupported = typeof ResizeObserver === 'function'
+
+// only used in jest tests
+export const resetResizeObserverSupported = () => {
+  resizeObserverSupported = typeof ResizeObserver === 'function'
+}
 
 export function calculateWidth (node, onUpdate) {
   let resizeObserver
-  /* istanbul ignore if */
   if (resizeObserverSupported) {
     resizeObserver = new ResizeObserver(entries => (
       onUpdate(entries[0].contentRect.width)
@@ -22,7 +26,6 @@ export function calculateWidth (node, onUpdate) {
 
   return {
     destroy () {
-      /* istanbul ignore if */
       if (resizeObserver) {
         resizeObserver.disconnect()
       }
diff --git a/test/spec/picker/noResizeObserver.test.js b/test/spec/picker/noResizeObserver.test.js
new file mode 100644
index 0000000..4ec51a7
--- /dev/null
+++ b/test/spec/picker/noResizeObserver.test.js
@@ -0,0 +1,65 @@
+import { groups } from '../../../src/picker/groups'
+import * as testingLibrary from '@testing-library/dom'
+import {
+  waitFor, getAllByRole,
+  getByRole, fireEvent
+} from '@testing-library/dom'
+import { ALL_EMOJI, basicAfterEach, basicBeforeEach, tick, truncatedEmoji } from '../shared'
+import Picker from '../../../src/picker/PickerElement'
+import Database from '../../../src/database/Database'
+import { resetResizeObserverSupported } from '../../../src/picker/utils/widthCalculator'
+
+// TODO: we can remove these tests when/if we stop supporting browsers without ResizeObserver
+// https://caniuse.com/resizeobserver
+
+describe('ResizeObserver unsupported', () => {
+  let picker
+  let container
+  let oldResizeObserver
+
+  beforeEach(async () => {
+    basicBeforeEach()
+
+    oldResizeObserver = global.ResizeObserver
+    delete global.ResizeObserver
+    resetResizeObserverSupported()
+
+    picker = new Picker({ dataSource: ALL_EMOJI })
+    document.body.appendChild(picker)
+    container = picker.shadowRoot.querySelector('.picker')
+    await tick(40)
+  })
+
+  afterEach(async () => {
+    await tick(40)
+    document.body.removeChild(picker)
+    await tick(40)
+    await new Database({ dataSource: ALL_EMOJI }).delete()
+    await tick(40)
+    basicAfterEach()
+
+    global.ResizeObserver = oldResizeObserver
+    resetResizeObserverSupported()
+  })
+
+  test('basic picker test', async () => {
+    const numInGroup1 = truncatedEmoji.filter(_ => _.group === 0).length
+    const numInGroup2 = truncatedEmoji.filter(_ => _.group === 1).length
+
+    await waitFor(() => expect(getByRole(container, 'button', { name: 'Choose a skin tone (currently Default)' })).toBeVisible())
+    expect(getAllByRole(container, 'tab')).toHaveLength(groups.length)
+
+    expect(getByRole(container, 'tab', { name: 'Smileys and emoticons', selected: true })).toBeVisible()
+    await waitFor(() => expect(
+      testingLibrary.getAllByRole(getByRole(container, 'tabpanel'), 'menuitem')).toHaveLength(numInGroup1)
+    )
+
+    expect(getByRole(container, 'tab', { name: 'People and body' })).toBeVisible()
+    fireEvent.click(getByRole(container, 'tab', { name: 'People and body' }))
+
+    await waitFor(() => expect(
+      testingLibrary.getAllByRole(getByRole(container, 'tabpanel'), 'menuitem')).toHaveLength(numInGroup2))
+
+    expect(getByRole(container, 'tab', { name: 'People and body', selected: true })).toBeVisible()
+  })
+})
diff --git a/yarn.lock b/yarn.lock
index 6145cbe..324ee36 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1500,6 +1500,13 @@
     tslib "^2.0.3"
     webcrypto-core "^1.1.8"
 
+"@polymer/polymer@^3.0.0":
+  version "3.4.1"
+  resolved "https://registry.yarnpkg.com/@polymer/polymer/-/polymer-3.4.1.tgz#333bef25711f8411bb5624fb3eba8212ef8bee96"
+  integrity sha512-KPWnhDZibtqKrUz7enIPOiO4ZQoJNOuLwqrhV2MXzIt3VVnUVJVG5ORz4Z2sgO+UZ+/UZnPD0jqY+jmw/+a9mQ==
+  dependencies:
+    "@webcomponents/shadycss" "^1.9.1"
+
 "@rollup/plugin-commonjs@^16.0.0":
   version "16.0.0"
   resolved "https://registry.yarnpkg.com/@rollup/plugin-commonjs/-/plugin-commonjs-16.0.0.tgz#169004d56cd0f0a1d0f35915d31a036b0efe281f"
@@ -1842,6 +1849,11 @@
   dependencies:
     "@types/node" "*"
 
+"@webcomponents/shadycss@^1.9.1":
+  version "1.10.2"
+  resolved "https://registry.yarnpkg.com/@webcomponents/shadycss/-/shadycss-1.10.2.tgz#40e03cab6dc5e12f199949ba2b79e02f183d1e7b"
+  integrity sha512-9Iseu8bRtecb0klvv+WXZOVZatsRkbaH7M97Z+f+Pt909R4lDfgUODAnra23DOZTpeMTAkVpf4m/FZztN7Ox1A==
+
 JSONStream@^1.0.4:
   version "1.3.5"
   resolved "https://registry.yarnpkg.com/JSONStream/-/JSONStream-1.3.5.tgz#3208c1f08d3a4d99261ab64f92302bc15e111ca0"
@@ -3419,6 +3431,12 @@ currently-unhandled@^0.4.1:
   dependencies:
     array-find-index "^1.0.1"
 
+"d2l-resize-aware@BrightspaceUI/resize-aware#semver:^1.2.2":
+  version "1.2.2"
+  resolved "https://codeload.github.com/BrightspaceUI/resize-aware/tar.gz/96ba3ac560380abfb753f128ac9a5c0992d7d723"
+  dependencies:
+    "@polymer/polymer" "^3.0.0"
+
 dargs@^4.0.1:
   version "4.1.0"
   resolved "https://registry.yarnpkg.com/dargs/-/dargs-4.1.0.tgz#03a9dbb4b5c2f139bf14ae53f0b8a2a6a86f4e17"