diff --git a/fixtures/dom/package.json b/fixtures/dom/package.json
index 3282c85fa58a..9bf118f0c29c 100644
--- a/fixtures/dom/package.json
+++ b/fixtures/dom/package.json
@@ -18,7 +18,7 @@
   },
   "scripts": {
     "start": "react-scripts start",
-    "prestart": "cp ../../build/node_modules/scheduler/umd/scheduler-unstable_mock.development.js ../../build/node_modules/scheduler/umd/scheduler-unstable_mock.production.min.js ../../build/node_modules/react/umd/react.development.js ../../build/node_modules/react-dom/umd/react-dom.development.js ../../build/node_modules/react/umd/react.production.min.js ../../build/node_modules/react-dom/umd/react-dom.production.min.js ../../build/node_modules/react-dom/umd/react-dom-server.browser.development.js ../../build/node_modules/react-dom/umd/react-dom-server.browser.production.min.js ../../build/node_modules/react-dom/umd/react-dom-test-utils.development.js ../../build/node_modules/react-dom/umd/react-dom-test-utils.production.min.js public/",
+    "prestart": "cp ../../build/node_modules/scheduler/umd/scheduler-unstable_mock.development.js ../../build/node_modules/scheduler/umd/scheduler-unstable_mock.production.min.js ../../build/node_modules/react/umd/react.development.js ../../build/node_modules/react-dom/umd/react-dom.development.js ../../build/node_modules/react/umd/react.production.min.js ../../build/node_modules/react-dom/umd/react-dom.production.min.js ../../build/node_modules/react-dom/umd/react-dom-server.browser.development.js ../../build/node_modules/react-dom/umd/react-dom-server.browser.production.min.js ../../build/node_modules/react-dom/umd/react-dom-test-utils.development.js ../../build/node_modules/react-dom/umd/react-dom-test-utils.production.min.js public/ && cp -a ../../build/node_modules/. node_modules",
     "build": "react-scripts build && cp build/index.html build/200.html",
     "test": "react-scripts test --env=jsdom",
     "eject": "react-scripts eject"
diff --git a/fixtures/dom/public/act-dom.html b/fixtures/dom/public/act-dom.html
index 2100026a5ba4..29152dc22dcb 100644
--- a/fixtures/dom/public/act-dom.html
+++ b/fixtures/dom/public/act-dom.html
@@ -15,7 +15,6 @@
   <script src='react-dom.development.js'></script>
   <script src='react-dom-test-utils.development.js'></script>
   <script>
-    async function run(){
       // from ReactTestUtilsAct-test.js
       function App() {
         let [state, setState] = React.useState(0);
@@ -23,23 +22,22 @@
           await null;
           setState(x => x + 1);
         }
-        React.useEffect(
-          () => {
-            ticker();
-          },
-          [Math.min(state, 4)],
-        );
+        React.useEffect(() => {
+          ticker();
+        }, [Math.min(state, 4)]);
         return state;
       }
-      const el = document.createElement('div');
-      await ReactTestUtils.act(async () => {
-        ReactDOM.render(React.createElement(App), el);
-      });
-      // all 5 ticks present and accounted for
-      console.log(el.innerHTML);
-    }
-    run();
-    
-  </script>
-</body>
+
+      async function testAsyncAct() {
+        const el = document.createElement("div");
+        await ReactTestUtils.act(async () => {
+          ReactDOM.render(React.createElement(App), el);
+        });
+        // all 5 ticks present and accounted for
+        console.log(el.innerHTML);
+      }
+
+      testAsyncAct();
+    </script>
+  </body>
 </html>
diff --git a/fixtures/dom/src/index.test.js b/fixtures/dom/src/index.test.js
new file mode 100644
index 000000000000..8c9f88600bc1
--- /dev/null
+++ b/fixtures/dom/src/index.test.js
@@ -0,0 +1,98 @@
+import React from 'react';
+import ReactDOM from 'react-dom';
+import TestUtils from 'react-dom/test-utils';
+import TestRenderer from 'react-test-renderer';
+
+let spy;
+beforeEach(() => {
+  spy = jest.spyOn(console, 'error').mockImplementation(() => {});
+});
+
+function confirmWarning() {
+  expect(spy).toHaveBeenCalledWith(
+    expect.stringContaining(
+      "It looks like you're using the wrong act() around your test interactions."
+    ),
+    ''
+  );
+}
+
+function App(props) {
+  return 'hello world';
+}
+
+it("doesn't warn when you use the right act + renderer: dom", () => {
+  TestUtils.act(() => {
+    TestUtils.renderIntoDocument(<App />);
+  });
+  expect(spy).not.toHaveBeenCalled();
+});
+
+it("doesn't warn when you use the right act + renderer: test", () => {
+  TestRenderer.act(() => {
+    TestRenderer.create(<App />);
+  });
+  expect(spy).not.toHaveBeenCalled();
+});
+
+it('works with createRoot().render combo', () => {
+  const root = ReactDOM.unstable_createRoot(document.createElement('div'));
+  TestRenderer.act(() => {
+    root.render(<App />);
+  });
+  confirmWarning();
+});
+
+it('warns when using the wrong act version - test + dom: render', () => {
+  TestRenderer.act(() => {
+    TestUtils.renderIntoDocument(<App />);
+  });
+  confirmWarning();
+});
+
+it('warns when using the wrong act version - test + dom: updates', () => {
+  let setCtr;
+  function Counter(props) {
+    const [ctr, _setCtr] = React.useState(0);
+    setCtr = _setCtr;
+    return ctr;
+  }
+  TestUtils.renderIntoDocument(<Counter />);
+  TestRenderer.act(() => {
+    setCtr(1);
+  });
+  confirmWarning();
+});
+
+it('warns when using the wrong act version - dom + test: .create()', () => {
+  TestUtils.act(() => {
+    TestRenderer.create(<App />);
+  });
+  confirmWarning();
+});
+
+it('warns when using the wrong act version - dom + test: .update()', () => {
+  let root;
+  // use the right one here so we don't get the first warning
+  TestRenderer.act(() => {
+    root = TestRenderer.create(<App key="one" />);
+  });
+  TestUtils.act(() => {
+    root.update(<App key="two" />);
+  });
+  confirmWarning();
+});
+
+it('warns when using the wrong act version - dom + test: updates', () => {
+  let setCtr;
+  function Counter(props) {
+    const [ctr, _setCtr] = React.useState(0);
+    setCtr = _setCtr;
+    return ctr;
+  }
+  const root = TestRenderer.create(<Counter />);
+  TestUtils.act(() => {
+    setCtr(1);
+  });
+  confirmWarning();
+});
diff --git a/package.json b/package.json
index 97998b6b6d4f..03ba206a0d3b 100644
--- a/package.json
+++ b/package.json
@@ -107,6 +107,7 @@
     "test-prod-build": "yarn test-build-prod",
     "test-build": "cross-env NODE_ENV=development jest --config ./scripts/jest/config.build.js",
     "test-build-prod": "cross-env NODE_ENV=production jest --config ./scripts/jest/config.build.js",
+    "test-dom-fixture": "cd fixtures/dom && yarn && yarn prestart && yarn test",
     "flow": "node ./scripts/tasks/flow.js",
     "flow-ci": "node ./scripts/tasks/flow-ci.js",
     "prettier": "node ./scripts/prettier/index.js write-changed",
diff --git a/packages/react-dom/src/__tests__/ReactTestUtilsAct-test.js b/packages/react-dom/src/__tests__/ReactTestUtilsAct-test.js
index fd32092584d0..be0a83253153 100644
--- a/packages/react-dom/src/__tests__/ReactTestUtilsAct-test.js
+++ b/packages/react-dom/src/__tests__/ReactTestUtilsAct-test.js
@@ -259,13 +259,13 @@ function runActTests(label, render, unmount) {
       it('warns if you return a value inside act', () => {
         expect(() => act(() => null)).toWarnDev(
           [
-            'The callback passed to act(...) function must return undefined, or a Promise.',
+            'The callback passed to act(...) function must return undefined or a Promise.',
           ],
           {withoutStack: true},
         );
         expect(() => act(() => 123)).toWarnDev(
           [
-            'The callback passed to act(...) function must return undefined, or a Promise.',
+            'The callback passed to act(...) function must return undefined or a Promise.',
           ],
           {withoutStack: true},
         );
@@ -274,7 +274,7 @@ function runActTests(label, render, unmount) {
       it('warns if you try to await a sync .act call', () => {
         expect(() => act(() => {}).then(() => {})).toWarnDev(
           [
-            'Do not await the result of calling act(...) with sync logic, it is not a Promise.',
+            'Do not await the result of calling a synchronous act(...), it is not a Promise.',
           ],
           {withoutStack: true},
         );
@@ -337,7 +337,7 @@ function runActTests(label, render, unmount) {
         if (__DEV__) {
           expect(console.error.calls.count()).toEqual(1);
           expect(console.error.calls.argsFor(0)[0]).toMatch(
-            'You called act(async () => ...) without await.',
+            'You called act(async () => ...) without awaiting its result.',
           );
         }
       });
diff --git a/packages/react-dom/src/test-utils/ReactTestUtils.js b/packages/react-dom/src/test-utils/ReactTestUtils.js
index f463cc4aa6a3..a9285db8e385 100644
--- a/packages/react-dom/src/test-utils/ReactTestUtils.js
+++ b/packages/react-dom/src/test-utils/ReactTestUtils.js
@@ -42,8 +42,9 @@ const [
   restoreStateIfNeeded,
   dispatchEvent,
   runEventsInBatch,
-  // eslint-disable-next-line no-unused-vars
+  /* eslint-disable no-unused-vars */
   flushPassiveEffects,
+  /* eslint-enable no-unused-vars */
 ] = ReactDOM.__SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED.Events;
 
 function Event(suffix) {}
diff --git a/packages/react-dom/src/test-utils/ReactTestUtilsAct.js b/packages/react-dom/src/test-utils/ReactTestUtilsAct.js
index 9667c1fbd5bb..602e28c095db 100644
--- a/packages/react-dom/src/test-utils/ReactTestUtilsAct.js
+++ b/packages/react-dom/src/test-utils/ReactTestUtilsAct.js
@@ -37,7 +37,7 @@ const [
 
 const batchedUpdates = ReactDOM.unstable_batchedUpdates;
 
-const {ReactShouldWarnActingUpdates} = ReactSharedInternals;
+const {ReactActingRendererSigil} = ReactSharedInternals;
 
 // this implementation should be exactly the same in
 // ReactTestUtilsAct.js, ReactTestRendererAct.js, createReactNoop.js
@@ -85,18 +85,20 @@ let actingUpdatesScopeDepth = 0;
 
 function act(callback: () => Thenable) {
   let previousActingUpdatesScopeDepth;
+  let previousActingUpdatesSigil;
   if (__DEV__) {
     previousActingUpdatesScopeDepth = actingUpdatesScopeDepth;
+    previousActingUpdatesSigil = ReactActingRendererSigil.current;
     actingUpdatesScopeDepth++;
-    ReactShouldWarnActingUpdates.current = true;
+    // we use the function flushPassiveEffects directly as the sigil,
+    // since it's unique to a renderer
+    ReactActingRendererSigil.current = flushPassiveEffects;
   }
 
   function onDone() {
     if (__DEV__) {
       actingUpdatesScopeDepth--;
-      if (actingUpdatesScopeDepth === 0) {
-        ReactShouldWarnActingUpdates.current = false;
-      }
+      ReactActingRendererSigil.current = previousActingUpdatesSigil;
       if (actingUpdatesScopeDepth > previousActingUpdatesScopeDepth) {
         // if it's _less than_ previousActingUpdatesScopeDepth, then we can assume the 'other' one has warned
         warningWithoutStack(
@@ -126,9 +128,10 @@ function act(callback: () => Thenable) {
             if (called === false) {
               warningWithoutStack(
                 null,
-                'You called act(async () => ...) without await. ' +
+                'You called act(async () => ...) without awaiting its result. ' +
                   'This could lead to unexpected testing behaviour, interleaving multiple act ' +
-                  'calls and mixing their scopes. You should - await act(async () => ...);',
+                  'calls and mixing their scopes. You should await asynchronous act() calls:\n' +
+                  'await act(async () => ...);\n',
               );
             }
           });
@@ -164,7 +167,7 @@ function act(callback: () => Thenable) {
       warningWithoutStack(
         result === undefined,
         'The callback passed to act(...) function ' +
-          'must return undefined, or a Promise. You returned %s',
+          'must return undefined or a Promise. You returned %s',
         result,
       );
     }
@@ -184,7 +187,8 @@ function act(callback: () => Thenable) {
         if (__DEV__) {
           warningWithoutStack(
             false,
-            'Do not await the result of calling act(...) with sync logic, it is not a Promise.',
+            'Do not await the result of calling a synchronous act(...), it is not a Promise. \n' +
+              'Remove the `await` statement before this act() call.',
           );
         }
         resolve();
diff --git a/packages/react-noop-renderer/src/createReactNoop.js b/packages/react-noop-renderer/src/createReactNoop.js
index e7bd09890a7b..bdef88ce3501 100644
--- a/packages/react-noop-renderer/src/createReactNoop.js
+++ b/packages/react-noop-renderer/src/createReactNoop.js
@@ -81,7 +81,7 @@ type TextInstance = {|
 |};
 type HostContext = Object;
 
-const {ReactShouldWarnActingUpdates} = ReactSharedInternals;
+const {ReactActingRendererSigil} = ReactSharedInternals;
 
 const NO_CONTEXT = {};
 const UPPERCASE_CONTEXT = {};
@@ -698,18 +698,20 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
 
   function act(callback: () => Thenable) {
     let previousActingUpdatesScopeDepth;
+    let previousActingUpdatesSigil;
     if (__DEV__) {
       previousActingUpdatesScopeDepth = actingUpdatesScopeDepth;
+      previousActingUpdatesSigil = ReactActingRendererSigil.current;
       actingUpdatesScopeDepth++;
-      ReactShouldWarnActingUpdates.current = true;
+      // we use the function flushPassiveEffects directly as the sigil,
+      // since it's unique to a renderer
+      ReactActingRendererSigil.current = flushPassiveEffects;
     }
 
     function onDone() {
       if (__DEV__) {
         actingUpdatesScopeDepth--;
-        if (actingUpdatesScopeDepth === 0) {
-          ReactShouldWarnActingUpdates.current = false;
-        }
+        ReactActingRendererSigil.current = previousActingUpdatesSigil;
         if (actingUpdatesScopeDepth > previousActingUpdatesScopeDepth) {
           // if it's _less than_ previousActingUpdatesScopeDepth, then we can assume the 'other' one has warned
           warningWithoutStack(
@@ -739,9 +741,10 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
               if (called === false) {
                 warningWithoutStack(
                   null,
-                  'You called act(async () => ...) without await. ' +
+                  'You called act(async () => ...) without awaiting its result. ' +
                     'This could lead to unexpected testing behaviour, interleaving multiple act ' +
-                    'calls and mixing their scopes. You should - await act(async () => ...);',
+                    'calls and mixing their scopes. You should await asynchronous act() calls:\n' +
+                    'await act(async () => ...);\n',
                 );
               }
             });
@@ -777,7 +780,7 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
         warningWithoutStack(
           result === undefined,
           'The callback passed to act(...) function ' +
-            'must return undefined, or a Promise. You returned %s',
+            'must return undefined or a Promise. You returned %s',
           result,
         );
       }
@@ -797,7 +800,8 @@ function createReactNoop(reconciler: Function, useMutation: boolean) {
           if (__DEV__) {
             warningWithoutStack(
               false,
-              'Do not await the result of calling act(...) with sync logic, it is not a Promise.',
+              'Do not await the result of calling a synchronous act(...), it is not a Promise. \n' +
+                'Remove the `await` statement before this act() call.',
             );
           }
           resolve();
diff --git a/packages/react-reconciler/src/ReactFiberHooks.js b/packages/react-reconciler/src/ReactFiberHooks.js
index f7eec92b3d2b..433efcfd0776 100644
--- a/packages/react-reconciler/src/ReactFiberHooks.js
+++ b/packages/react-reconciler/src/ReactFiberHooks.js
@@ -36,6 +36,7 @@ import {
   requestCurrentTime,
   warnIfNotCurrentlyActingUpdatesInDev,
   markRenderEventTimeAndConfig,
+  warnIfNotScopedWithMatchingAct,
 } from './ReactFiberScheduler';
 
 import invariant from 'shared/invariant';
@@ -1211,6 +1212,7 @@ function dispatchAction<S, A>(
       // further, this isn't a test file, so flow doesn't recognize the symbol. So...
       // $FlowExpectedError - because requirements don't give a damn about your type sigs.
       if ('undefined' !== typeof jest) {
+        warnIfNotScopedWithMatchingAct(fiber);
         warnIfNotCurrentlyActingUpdatesInDev(fiber);
       }
     }
diff --git a/packages/react-reconciler/src/ReactFiberReconciler.js b/packages/react-reconciler/src/ReactFiberReconciler.js
index 84291f4b7a16..b94c014369f0 100644
--- a/packages/react-reconciler/src/ReactFiberReconciler.js
+++ b/packages/react-reconciler/src/ReactFiberReconciler.js
@@ -55,6 +55,7 @@ import {
   interactiveUpdates,
   flushInteractiveUpdates,
   flushPassiveEffects,
+  warnIfNotScopedWithMatchingAct,
 } from './ReactFiberScheduler';
 import {createUpdate, enqueueUpdate} from './ReactUpdateQueue';
 import ReactFiberInstrumentation from './ReactFiberInstrumentation';
@@ -302,6 +303,14 @@ export function updateContainer(
 ): ExpirationTime {
   const current = container.current;
   const currentTime = requestCurrentTime();
+  if (__DEV__) {
+    // jest isn't a 'global', it's just exposed to tests via a wrapped function
+    // further, this isn't a test file, so flow doesn't recognize the symbol. So...
+    // $FlowExpectedError - because requirements don't give a damn about your type sigs.
+    if ('undefined' !== typeof jest) {
+      warnIfNotScopedWithMatchingAct(current);
+    }
+  }
   const suspenseConfig = requestCurrentSuspenseConfig();
   const expirationTime = computeExpirationForFiber(
     currentTime,
diff --git a/packages/react-reconciler/src/ReactFiberScheduler.js b/packages/react-reconciler/src/ReactFiberScheduler.js
index 9fd797baa10d..562a46e4a582 100644
--- a/packages/react-reconciler/src/ReactFiberScheduler.js
+++ b/packages/react-reconciler/src/ReactFiberScheduler.js
@@ -175,7 +175,7 @@ const ceil = Math.ceil;
 const {
   ReactCurrentDispatcher,
   ReactCurrentOwner,
-  ReactShouldWarnActingUpdates,
+  ReactActingRendererSigil,
 } = ReactSharedInternals;
 
 type WorkPhase = 0 | 1 | 2 | 3 | 4 | 5;
@@ -2255,23 +2255,58 @@ function warnAboutInvalidUpdatesOnClassComponentsInDEV(fiber) {
   }
 }
 
+export function warnIfNotScopedWithMatchingAct(fiber: Fiber): void {
+  if (__DEV__) {
+    if (
+      ReactActingRendererSigil.current !== null &&
+      // use the function flushPassiveEffects directly as the sigil
+      // so this comparison is expected here
+      ReactActingRendererSigil.current !== flushPassiveEffects
+    ) {
+      // it looks like we're using the wrong matching act(), so log a warning
+      warningWithoutStack(
+        false,
+        "It looks like you're using the wrong act() around your test interactions.\n" +
+          'Be sure to use the matching version of act() corresponding to your renderer:\n\n' +
+          '// for react-dom:\n' +
+          "import {act} from 'react-test-utils';\n" +
+          '//...\n' +
+          'act(() => ...);\n\n' +
+          '// for react-test-renderer:\n' +
+          "import TestRenderer from 'react-test-renderer';\n" +
+          'const {act} = TestRenderer;\n' +
+          '//...\n' +
+          'act(() => ...);' +
+          '%s',
+        getStackByFiberInDevAndProd(fiber),
+      );
+    }
+  }
+}
+
+// in a test-like environment, we want to warn if dispatchAction() is
+// called outside of a TestUtils.act(...)/batchedUpdates/render call.
+// so we have a a step counter for when we descend/ascend from
+// act() calls, and test on it for when to warn
+// It's a tuple with a single value. Look into ReactTestUtilsAct as an
+// example of how we change the value
+
 function warnIfNotCurrentlyActingUpdatesInDEV(fiber: Fiber): void {
   if (__DEV__) {
     if (
       workPhase === NotWorking &&
-      ReactShouldWarnActingUpdates.current === false
+      ReactActingRendererSigil.current !== flushPassiveEffects
     ) {
       warningWithoutStack(
         false,
         'An update to %s inside a test was not wrapped in act(...).\n\n' +
           'When testing, code that causes React state updates should be ' +
-          'wrapped into act(...):\n\n' +
-          'act(() => {\n' +
+          'wrapped inside act(...):\n\n' +
+          'await act(async () => {\n' +
           '  /* fire events that update state */\n' +
           '});\n' +
           '/* assert on the output */\n\n' +
-          "This ensures that you're testing the behavior the user would see " +
-          'in the browser.' +
+          "This ensures that you're testing behavior similar to what a user would experience.\n" +
           ' Learn more at https://fb.me/react-wrap-tests-with-act' +
           '%s',
         getComponentName(fiber.type),
diff --git a/packages/react-test-renderer/src/ReactTestRendererAct.js b/packages/react-test-renderer/src/ReactTestRendererAct.js
index a3d1e4e9cc46..886e4d2beabb 100644
--- a/packages/react-test-renderer/src/ReactTestRendererAct.js
+++ b/packages/react-test-renderer/src/ReactTestRendererAct.js
@@ -18,7 +18,7 @@ import {warnAboutMissingMockScheduler} from 'shared/ReactFeatureFlags';
 import enqueueTask from 'shared/enqueueTask';
 import * as Scheduler from 'scheduler';
 
-const {ReactShouldWarnActingUpdates} = ReactSharedInternals;
+const {ReactActingRendererSigil} = ReactSharedInternals;
 
 // this implementation should be exactly the same in
 // ReactTestUtilsAct.js, ReactTestRendererAct.js, createReactNoop.js
@@ -66,18 +66,20 @@ let actingUpdatesScopeDepth = 0;
 
 function act(callback: () => Thenable) {
   let previousActingUpdatesScopeDepth;
+  let previousActingUpdatesSigil;
   if (__DEV__) {
     previousActingUpdatesScopeDepth = actingUpdatesScopeDepth;
+    previousActingUpdatesSigil = ReactActingRendererSigil.current;
     actingUpdatesScopeDepth++;
-    ReactShouldWarnActingUpdates.current = true;
+    // we use the function flushPassiveEffects directly as the sigil,
+    // since it's unique to a renderer
+    ReactActingRendererSigil.current = flushPassiveEffects;
   }
 
   function onDone() {
     if (__DEV__) {
       actingUpdatesScopeDepth--;
-      if (actingUpdatesScopeDepth === 0) {
-        ReactShouldWarnActingUpdates.current = false;
-      }
+      ReactActingRendererSigil.current = previousActingUpdatesSigil;
       if (actingUpdatesScopeDepth > previousActingUpdatesScopeDepth) {
         // if it's _less than_ previousActingUpdatesScopeDepth, then we can assume the 'other' one has warned
         warningWithoutStack(
@@ -107,9 +109,10 @@ function act(callback: () => Thenable) {
             if (called === false) {
               warningWithoutStack(
                 null,
-                'You called act(async () => ...) without await. ' +
+                'You called act(async () => ...) without awaiting its result. ' +
                   'This could lead to unexpected testing behaviour, interleaving multiple act ' +
-                  'calls and mixing their scopes. You should - await act(async () => ...);',
+                  'calls and mixing their scopes. You should await asynchronous act() calls:\n' +
+                  'await act(async () => ...);\n',
               );
             }
           });
@@ -145,7 +148,7 @@ function act(callback: () => Thenable) {
       warningWithoutStack(
         result === undefined,
         'The callback passed to act(...) function ' +
-          'must return undefined, or a Promise. You returned %s',
+          'must return undefined or a Promise. You returned %s',
         result,
       );
     }
@@ -165,7 +168,8 @@ function act(callback: () => Thenable) {
         if (__DEV__) {
           warningWithoutStack(
             false,
-            'Do not await the result of calling act(...) with sync logic, it is not a Promise.',
+            'Do not await the result of calling a synchronous act(...), it is not a Promise. \n' +
+              'Remove the `await` statement before this act() call.',
           );
         }
         resolve();
diff --git a/packages/react/src/ReactActingRendererSigil.js b/packages/react/src/ReactActingRendererSigil.js
new file mode 100644
index 000000000000..a40ecca4c660
--- /dev/null
+++ b/packages/react/src/ReactActingRendererSigil.js
@@ -0,0 +1,19 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+/**
+ * Used by act() to track whether you're outside an act() scope.
+ * We use a renderer's flushPassiveEffects as the sigil value
+ * so we can track identity of the renderer.
+ */
+
+const ReactActingRendererSigil = {
+  current: (null: null | (() => boolean)),
+};
+export default ReactActingRendererSigil;
diff --git a/packages/react/src/ReactSharedInternals.js b/packages/react/src/ReactSharedInternals.js
index 1bc95cffaad4..de4a14adb3db 100644
--- a/packages/react/src/ReactSharedInternals.js
+++ b/packages/react/src/ReactSharedInternals.js
@@ -10,13 +10,13 @@ import ReactCurrentDispatcher from './ReactCurrentDispatcher';
 import ReactCurrentBatchConfig from './ReactCurrentBatchConfig';
 import ReactCurrentOwner from './ReactCurrentOwner';
 import ReactDebugCurrentFrame from './ReactDebugCurrentFrame';
+import ReactActingRendererSigil from './ReactActingRendererSigil';
 
 const ReactSharedInternals = {
   ReactCurrentDispatcher,
   ReactCurrentBatchConfig,
   ReactCurrentOwner,
-  // used by act()
-  ReactShouldWarnActingUpdates: {current: false},
+  ReactActingRendererSigil,
   // Used by renderers to avoid bundling object-assign twice in UMD bundles:
   assign,
 };
diff --git a/scripts/circleci/test_entry_point.sh b/scripts/circleci/test_entry_point.sh
index 5bf568028aeb..a1343ce4cf98 100755
--- a/scripts/circleci/test_entry_point.sh
+++ b/scripts/circleci/test_entry_point.sh
@@ -30,6 +30,7 @@ if [ $((2 % CIRCLE_NODE_TOTAL)) -eq "$CIRCLE_NODE_INDEX" ]; then
   COMMANDS_TO_RUN+=('./scripts/circleci/build.sh')
   COMMANDS_TO_RUN+=('yarn test-build --maxWorkers=2')
   COMMANDS_TO_RUN+=('yarn test-build-prod --maxWorkers=2')
+  COMMANDS_TO_RUN+=('yarn test-dom-fixture')
   COMMANDS_TO_RUN+=('cp ./scripts/rollup/results.json ./build/bundle-sizes.json')
   COMMANDS_TO_RUN+=('node ./scripts/tasks/danger')
   COMMANDS_TO_RUN+=('./scripts/circleci/upload_build.sh')