diff --git a/package.json b/package.json
index b64c6a8c27..0db04b2e5d 100644
--- a/package.json
+++ b/package.json
@@ -157,6 +157,9 @@
     "coverageDirectory": "coverage",
     "testMatch": [
       "<rootDir>/tests/**/*.test.(ts|tsx)"
+    ],
+    "setupFiles": [
+      "<rootDir>/tests/_setup.js"
     ]
   }
 }
diff --git a/src/useMeasure.ts b/src/useMeasure.ts
index 37af79aae8..57d5c6d3fb 100644
--- a/src/useMeasure.ts
+++ b/src/useMeasure.ts
@@ -1,5 +1,4 @@
 import { useState, useMemo } from 'react';
-import ResizeObserver from 'resize-observer-polyfill';
 import useIsomorphicLayoutEffect from './useIsomorphicLayoutEffect';
 
 export type UseMeasureRect = Pick<
@@ -26,7 +25,7 @@ const useMeasure = (): UseMeasureResult => {
 
   const observer = useMemo(
     () =>
-      new ResizeObserver(entries => {
+      new (window as any).ResizeObserver(entries => {
         if (entries[0]) {
           const { x, y, width, height, top, left, bottom, right } = entries[0].contentRect;
           setRect({ x, y, width, height, top, left, bottom, right });
diff --git a/tests/_setup.js b/tests/_setup.js
new file mode 100644
index 0000000000..b4816e4044
--- /dev/null
+++ b/tests/_setup.js
@@ -0,0 +1,5 @@
+window.ResizeObserver = class ResizeObserver {
+  constructor() {}
+  observe() {}
+  disconnect() {}
+};
diff --git a/tests/useMeasure.test.ts b/tests/useMeasure.test.ts
index 6d9da805b3..33c6f805d4 100644
--- a/tests/useMeasure.test.ts
+++ b/tests/useMeasure.test.ts
@@ -1,88 +1,79 @@
-import { act, renderHook } from '@testing-library/react-hooks';
-import useMeasure, { ContentRect } from '../src/useMeasure';
-
-interface Entry {
-  target: HTMLElement;
-  contentRect: ContentRect;
-}
-
-jest.mock('resize-observer-polyfill', () => {
-  return class ResizeObserver {
-    private cb: (entries: Entry[]) => void;
-    private map: WeakMap<HTMLElement, any>;
-    private targets: HTMLElement[];
-    constructor(cb: () => void) {
-      this.cb = cb;
-      this.map = new WeakMap();
-      this.targets = [];
-    }
-    public disconnect() {
-      this.targets.map(target => {
-        const originMethod = this.map.get(target);
-        target.setAttribute = originMethod;
-        this.map.delete(target);
-      });
-    }
-    public observe(target: HTMLElement) {
-      const method = 'setAttribute';
-      const originMethod = target[method];
-      this.map.set(target, originMethod);
-      this.targets.push(target);
-      target[method] = (...args) => {
-        const [attrName, value] = args;
-        if (attrName === 'style') {
-          const rect: DOMRectReadOnly = {
-            x: 0,
-            y: 0,
-            top: 0,
-            left: 0,
-            right: 0,
-            bottom: 0,
-            width: 0,
-            height: 0,
-          } as DOMRectReadOnly;
-          value.split(';').map(kv => {
-            const [key, v] = kv.split(':');
-            if (['top', 'bottom', 'left', 'right', 'width', 'height'].includes(key)) {
-              rect[key] = parseInt(v, 10);
-            }
-          });
-          target.getBoundingClientRect = () => rect;
-        }
-        originMethod.apply(target, args);
-        this.fireCallback();
-      };
-    }
-    private fireCallback() {
-      if (this.cb) {
-        this.cb(
-          this.targets.map(target => {
-            return {
-              target,
-              contentRect: target.getBoundingClientRect() as ContentRect,
-            };
-          })
-        );
-      }
+import { renderHook, act } from '@testing-library/react-hooks';
+import useMeasure, { UseMeasureRef } from '../src/useMeasure';
+
+it('by default, state defaults every value to -1', () => {
+  const { result } = renderHook(() => useMeasure());
+
+  act(() => {
+    const div = document.createElement('div');
+    (result.current[0] as UseMeasureRef)(div);
+  });
+
+  expect(result.current[1]).toMatchObject({
+    width: -1,
+    height: -1,
+    top: -1,
+    bottom: -1,
+    left: -1,
+    right: -1,
+  });
+});
+
+it('synchronously sets up ResizeObserver listener', () => {
+  let listener: ((rect: any) => void) | undefined = undefined;
+  (window as any).ResizeObserver = class ResizeObserver {
+    constructor(ls) {
+      listener = ls;
     }
+    observe() {}
+    disconnect() {}
   };
+
+  const { result } = renderHook(() => useMeasure());
+  
+  act(() => {
+    const div = document.createElement('div');
+    (result.current[0] as UseMeasureRef)(div);
+  });
+
+  expect(typeof listener).toBe('function');
 });
 
-it('reacts to changes in size of any of the observed elements', () => {
+it('tracks rectangle of a DOM element', () => {
+  let listener: ((rect: any) => void) | undefined = undefined;
+  (window as any).ResizeObserver = class ResizeObserver {
+    constructor(ls) {
+      listener = ls;
+    }
+    observe() {}
+    disconnect() {}
+  };
+
   const { result } = renderHook(() => useMeasure());
-  const div = document.createElement('div');
-  result.current[0](div);
-  expect(result.current[1]).toMatchObject({
-    width: 0,
-    height: 0,
-    top: 0,
-    bottom: 0,
-    left: 0,
-    right: 0,
+  
+  act(() => {
+    const div = document.createElement('div');
+    (result.current[0] as UseMeasureRef)(div);
+  });
+  
+  act(() => {
+    listener!([{
+      contentRect: {
+        x: 1,
+        y: 2,
+        width: 200,
+        height: 200,
+        top: 100,
+        bottom: 0,
+        left: 100,
+        right: 0,
+      }
+    }]);
   });
-  act(() => div.setAttribute('style', 'width:200px;height:200px;top:100;left:100'));
 
   expect(result.current[1]).toMatchObject({
+    x: 1,
+    y: 2,
     width: 200,
     height: 200,
     top: 100,
@@ -91,3 +82,97 @@ it('reacts to changes in size of any of the observed elements', () => {
     right: 0,
   });
 });
+
+it('tracks multiple updates', () => {
+  let listener: ((rect: any) => void) | undefined = undefined;
+  (window as any).ResizeObserver = class ResizeObserver {
+    constructor(ls) {
+      listener = ls;
+    }
+    observe() {}
+    disconnect() {}
+  };
+
+  const { result } = renderHook(() => useMeasure());
+  
+  act(() => {
+    const div = document.createElement('div');
+    (result.current[0] as UseMeasureRef)(div);
+  });
+  
+  act(() => {
+    listener!([{
+      contentRect: {
+        x: 1,
+        y: 1,
+        width: 1,
+        height: 1,
+        top: 1,
+        bottom: 1,
+        left: 1,
+        right: 1,
+      }
+    }]);
+  });
+
+  expect(result.current[1]).toMatchObject({
+    x: 1,
+    y: 1,
+    width: 1,
+    height: 1,
+    top: 1,
+    bottom: 1,
+    left: 1,
+    right: 1,
+  });
+  
+  act(() => {
+    listener!([{
+      contentRect: {
+        x: 2,
+        y: 2,
+        width: 2,
+        height: 2,
+        top: 2,
+        bottom: 2,
+        left: 2,
+        right: 2,
+      }
+    }]);
+  });
+
+  expect(result.current[1]).toMatchObject({
+    x: 2,
+    y: 2,
+    width: 2,
+    height: 2,
+    top: 2,
+    bottom: 2,
+    left: 2,
+    right: 2,
+  });
+});
+
+it('calls .disconnect() on ResizeObserver when component unmounts', () => {
+  const disconnect = jest.fn();
+  (window as any).ResizeObserver = class ResizeObserver {
+    constructor() {}
+    observe() {}
+    disconnect() {
+      disconnect();
+    }
+  };
+
+  const { result, unmount } = renderHook(() => useMeasure());
+  
+  act(() => {
+    const div = document.createElement('div');
+    (result.current[0] as UseMeasureRef)(div);
+  });
+
+  expect(disconnect).toHaveBeenCalledTimes(0);
+
+  unmount();
+
+  expect(disconnect).toHaveBeenCalledTimes(1);
+});