diff --git a/packages/react-dom/src/client/ToStringValue.js b/packages/react-dom/src/client/ToStringValue.js
index 1cb8f60f0b5e7..cf4a173e1399d 100644
--- a/packages/react-dom/src/client/ToStringValue.js
+++ b/packages/react-dom/src/client/ToStringValue.js
@@ -38,22 +38,6 @@ export function getToStringValue(value: mixed): ToStringValue {
   }
 }
 
-/**
- * Returns true only if Trusted Types are available in global object and the value is a trusted type.
- */
-let isTrustedTypesValue: (value: any) => boolean;
-// $FlowExpectedError - TrustedTypes are defined only in some browsers or with polyfill
-if (enableTrustedTypesIntegration && typeof trustedTypes !== 'undefined') {
-  isTrustedTypesValue = (value: any) =>
-    trustedTypes.isHTML(value) ||
-    trustedTypes.isScript(value) ||
-    trustedTypes.isScriptURL(value) ||
-    // TrustedURLs are deprecated and will be removed soon: https://github.com/WICG/trusted-types/pull/204
-    (trustedTypes.isURL && trustedTypes.isURL(value));
-} else {
-  isTrustedTypesValue = () => false;
-}
-
 /** Trusted value is a wrapper for "safe" values which can be assigned to DOM execution sinks. */
 export opaque type TrustedValue: {toString(): string, valueOf(): string} = {
   toString(): string,
@@ -67,15 +51,21 @@ export opaque type TrustedValue: {toString(): string, valueOf(): string} = {
  *
  * If application uses Trusted Types we don't stringify trusted values, but preserve them as objects.
  */
-export function toStringOrTrustedType(value: any): string | TrustedValue {
-  if (
-    enableTrustedTypesIntegration &&
-    // fast-path string values as it's most frequent usage of the function
-    typeof value !== 'string' &&
-    isTrustedTypesValue(value)
-  ) {
-    return value;
-  } else {
-    return '' + value;
-  }
+export let toStringOrTrustedType: any => string | TrustedValue = toString;
+if (enableTrustedTypesIntegration && typeof trustedTypes !== 'undefined') {
+  const isHTML = trustedTypes.isHTML;
+  const isScript = trustedTypes.isScript;
+  const isScriptURL = trustedTypes.isScriptURL;
+  // TrustedURLs are deprecated and will be removed soon: https://github.com/WICG/trusted-types/pull/204
+  const isURL = trustedTypes.isURL ? trustedTypes.isURL : value => false;
+  toStringOrTrustedType = value => {
+    if (
+      typeof value === 'object' &&
+      (isHTML(value) || isScript(value) || isScriptURL(value) || isURL(value))
+    ) {
+      // Pass Trusted Types through.
+      return value;
+    }
+    return toString(value);
+  };
 }
diff --git a/packages/react-dom/src/client/__tests__/trustedTypes-test.internal.js b/packages/react-dom/src/client/__tests__/trustedTypes-test.internal.js
index 3a9eb4c15d16c..b3511b43dc3ab 100644
--- a/packages/react-dom/src/client/__tests__/trustedTypes-test.internal.js
+++ b/packages/react-dom/src/client/__tests__/trustedTypes-test.internal.js
@@ -1,13 +1,28 @@
+/**
+ * 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.
+ *
+ * @emails react-core
+ */
+
+'use strict';
+
 describe('when Trusted Types are available in global object', () => {
   let React;
   let ReactDOM;
   let ReactFeatureFlags;
   let container;
+  let ttObject1;
+  let ttObject2;
 
   beforeEach(() => {
+    jest.resetModules();
     container = document.createElement('div');
+    const fakeTTObjects = new Set();
     window.trustedTypes = {
-      isHTML: () => true,
+      isHTML: value => fakeTTObjects.has(value),
       isScript: () => false,
       isScriptURL: () => false,
     };
@@ -15,28 +30,151 @@ describe('when Trusted Types are available in global object', () => {
     ReactFeatureFlags.enableTrustedTypesIntegration = true;
     React = require('react');
     ReactDOM = require('react-dom');
+    ttObject1 = {
+      toString() {
+        return '<b>Hi</b>';
+      },
+    };
+    ttObject2 = {
+      toString() {
+        return '<b>Bye</b>';
+      },
+    };
+    fakeTTObjects.add(ttObject1);
+    fakeTTObjects.add(ttObject2);
   });
 
   afterEach(() => {
     delete window.trustedTypes;
-    ReactFeatureFlags.enableTrustedTypesIntegration = false;
   });
 
-  it('should not stringify trusted values', () => {
-    const trustedObject = {toString: () => 'I look like a trusted object'};
-    class Component extends React.Component {
-      state = {inner: undefined};
-      render() {
-        return <div dangerouslySetInnerHTML={{__html: this.state.inner}} />;
-      }
+  it('should not stringify trusted values for dangerouslySetInnerHTML', () => {
+    let innerHTMLDescriptor = Object.getOwnPropertyDescriptor(
+      Element.prototype,
+      'innerHTML',
+    );
+    try {
+      const innerHTMLCalls = [];
+      Object.defineProperty(Element.prototype, 'innerHTML', {
+        get() {
+          return innerHTMLDescriptor.get.apply(this, arguments);
+        },
+        set(value) {
+          innerHTMLCalls.push(value);
+          return innerHTMLDescriptor.set.apply(this, arguments);
+        },
+      });
+      ReactDOM.render(
+        <div dangerouslySetInnerHTML={{__html: ttObject1}} />,
+        container,
+      );
+      expect(container.innerHTML).toBe('<div><b>Hi</b></div>');
+      expect(innerHTMLCalls.length).toBe(1);
+      // Ensure it didn't get stringified when passed to a DOM sink:
+      expect(innerHTMLCalls[0]).toBe(ttObject1);
+
+      innerHTMLCalls.length = 0;
+      ReactDOM.render(
+        <div dangerouslySetInnerHTML={{__html: ttObject2}} />,
+        container,
+      );
+      expect(container.innerHTML).toBe('<div><b>Bye</b></div>');
+      expect(innerHTMLCalls.length).toBe(1);
+      // Ensure it didn't get stringified when passed to a DOM sink:
+      expect(innerHTMLCalls[0]).toBe(ttObject2);
+    } finally {
+      Object.defineProperty(
+        Element.prototype,
+        'innerHTML',
+        innerHTMLDescriptor,
+      );
+    }
+  });
+
+  it('should not stringify trusted values for setAttribute (unknown attribute)', () => {
+    let setAttribute = Element.prototype.setAttribute;
+    try {
+      const setAttributeCalls = [];
+      Element.prototype.setAttribute = function(name, value) {
+        setAttributeCalls.push([this, name.toLowerCase(), value]);
+        return setAttribute.apply(this, arguments);
+      };
+      ReactDOM.render(<div data-foo={ttObject1} />, container);
+      expect(container.innerHTML).toBe('<div data-foo="<b>Hi</b>"></div>');
+      expect(setAttributeCalls.length).toBe(1);
+      expect(setAttributeCalls[0][0]).toBe(container.firstChild);
+      expect(setAttributeCalls[0][1]).toBe('data-foo');
+      // Ensure it didn't get stringified when passed to a DOM sink:
+      expect(setAttributeCalls[0][2]).toBe(ttObject1);
+
+      setAttributeCalls.length = 0;
+      ReactDOM.render(<div data-foo={ttObject2} />, container);
+      expect(setAttributeCalls.length).toBe(1);
+      expect(setAttributeCalls[0][0]).toBe(container.firstChild);
+      expect(setAttributeCalls[0][1]).toBe('data-foo');
+      // Ensure it didn't get stringified when passed to a DOM sink:
+      expect(setAttributeCalls[0][2]).toBe(ttObject2);
+    } finally {
+      Element.prototype.setAttribute = setAttribute;
     }
+  });
+
+  it('should not stringify trusted values for setAttribute (known attribute)', () => {
+    let setAttribute = Element.prototype.setAttribute;
+    try {
+      const setAttributeCalls = [];
+      Element.prototype.setAttribute = function(name, value) {
+        setAttributeCalls.push([this, name.toLowerCase(), value]);
+        return setAttribute.apply(this, arguments);
+      };
+      ReactDOM.render(<div className={ttObject1} />, container);
+      expect(container.innerHTML).toBe('<div class="<b>Hi</b>"></div>');
+      expect(setAttributeCalls.length).toBe(1);
+      expect(setAttributeCalls[0][0]).toBe(container.firstChild);
+      expect(setAttributeCalls[0][1]).toBe('class');
+      // Ensure it didn't get stringified when passed to a DOM sink:
+      expect(setAttributeCalls[0][2]).toBe(ttObject1);
+
+      setAttributeCalls.length = 0;
+      ReactDOM.render(<div className={ttObject2} />, container);
+      expect(setAttributeCalls.length).toBe(1);
+      expect(setAttributeCalls[0][0]).toBe(container.firstChild);
+      expect(setAttributeCalls[0][1]).toBe('class');
+      // Ensure it didn't get stringified when passed to a DOM sink:
+      expect(setAttributeCalls[0][2]).toBe(ttObject2);
+    } finally {
+      Element.prototype.setAttribute = setAttribute;
+    }
+  });
 
-    const isHTMLSpy = jest.spyOn(window.trustedTypes, ['isHTML']);
-    const instance = ReactDOM.render(<Component />, container);
-    instance.setState({inner: trustedObject});
+  it('should not stringify trusted values for setAttributeNS', () => {
+    let setAttributeNS = Element.prototype.setAttributeNS;
+    try {
+      const setAttributeNSCalls = [];
+      Element.prototype.setAttributeNS = function(ns, name, value) {
+        setAttributeNSCalls.push([this, ns, name, value]);
+        return setAttributeNS.apply(this, arguments);
+      };
+      ReactDOM.render(<svg xlinkHref={ttObject1} />, container);
+      expect(container.innerHTML).toBe('<svg xlink:href="<b>Hi</b>"></svg>');
+      expect(setAttributeNSCalls.length).toBe(1);
+      expect(setAttributeNSCalls[0][0]).toBe(container.firstChild);
+      expect(setAttributeNSCalls[0][1]).toBe('http://www.w3.org/1999/xlink');
+      expect(setAttributeNSCalls[0][2]).toBe('xlink:href');
+      // Ensure it didn't get stringified when passed to a DOM sink:
+      expect(setAttributeNSCalls[0][3]).toBe(ttObject1);
 
-    expect(container.firstChild.innerHTML).toBe(trustedObject.toString());
-    expect(isHTMLSpy).toHaveBeenCalledWith(trustedObject);
+      setAttributeNSCalls.length = 0;
+      ReactDOM.render(<svg xlinkHref={ttObject2} />, container);
+      expect(setAttributeNSCalls.length).toBe(1);
+      expect(setAttributeNSCalls[0][0]).toBe(container.firstChild);
+      expect(setAttributeNSCalls[0][1]).toBe('http://www.w3.org/1999/xlink');
+      expect(setAttributeNSCalls[0][2]).toBe('xlink:href');
+      // Ensure it didn't get stringified when passed to a DOM sink:
+      expect(setAttributeNSCalls[0][3]).toBe(ttObject2);
+    } finally {
+      Element.prototype.setAttributeNS = setAttributeNS;
+    }
   });
 
   describe('dangerouslySetInnerHTML in svg elements in Internet Explorer', () => {
@@ -81,6 +219,7 @@ describe('when Trusted Types are available in global object', () => {
           "You can try to wrap your svg element inside a div and use 'dangerouslySetInnerHTML' " +
           'on the enclosing div instead.',
       );
+      expect(container.innerHTML).toBe('<svg>unsafe html</svg>');
     });
   });
 
@@ -95,7 +234,7 @@ describe('when Trusted Types are available in global object', () => {
         '    in script (at **)',
     );
 
-    // check that the warning is print only once
+    // check that the warning is printed only once
     ReactDOM.render(<script>alert("I am not executed")</script>, container);
   });
 });
diff --git a/packages/react-dom/src/client/setInnerHTML.js b/packages/react-dom/src/client/setInnerHTML.js
index 4fa94a4e95c92..2b3227bdcaba1 100644
--- a/packages/react-dom/src/client/setInnerHTML.js
+++ b/packages/react-dom/src/client/setInnerHTML.js
@@ -27,23 +27,26 @@ const setInnerHTML = createMicrosoftUnsafeLocalFunction(function(
   node: Element,
   html: string | TrustedValue,
 ): void {
-  // IE does not have innerHTML for SVG nodes, so instead we inject the
-  // new markup in a temp node and then move the child nodes across into
-  // the target node
   if (node.namespaceURI === Namespaces.svg) {
-    if (enableTrustedTypesIntegration && __DEV__) {
-      warning(
-        // $FlowExpectedError - trustedTypes are defined only in some browsers or with polyfill
-        typeof trustedTypes === 'undefined',
-        "Using 'dangerouslySetInnerHTML' in an svg element with " +
-          'Trusted Types enabled in an Internet Explorer will cause ' +
-          'the trusted value to be converted to string. Assigning string ' +
-          "to 'innerHTML' will throw an error if Trusted Types are enforced. " +
-          "You can try to wrap your svg element inside a div and use 'dangerouslySetInnerHTML' " +
-          'on the enclosing div instead.',
-      );
+    if (__DEV__) {
+      if (enableTrustedTypesIntegration) {
+        // TODO: reconsider the text of this warning and when it should show
+        // before enabling the feature flag.
+        warning(
+          typeof trustedTypes === 'undefined',
+          "Using 'dangerouslySetInnerHTML' in an svg element with " +
+            'Trusted Types enabled in an Internet Explorer will cause ' +
+            'the trusted value to be converted to string. Assigning string ' +
+            "to 'innerHTML' will throw an error if Trusted Types are enforced. " +
+            "You can try to wrap your svg element inside a div and use 'dangerouslySetInnerHTML' " +
+            'on the enclosing div instead.',
+        );
+      }
     }
     if (!('innerHTML' in node)) {
+      // IE does not have innerHTML for SVG nodes, so instead we inject the
+      // new markup in a temp node and then move the child nodes across into
+      // the target node
       reusableSVGContainer =
         reusableSVGContainer || document.createElement('div');
       reusableSVGContainer.innerHTML =
@@ -55,12 +58,10 @@ const setInnerHTML = createMicrosoftUnsafeLocalFunction(function(
       while (svgNode.firstChild) {
         node.appendChild(svgNode.firstChild);
       }
-    } else {
-      node.innerHTML = (html: any);
+      return;
     }
-  } else {
-    node.innerHTML = (html: any);
   }
+  node.innerHTML = (html: any);
 });
 
 export default setInnerHTML;
diff --git a/scripts/flow/environment.js b/scripts/flow/environment.js
index 8a0806c4a9744..8eeda9784000d 100644
--- a/scripts/flow/environment.js
+++ b/scripts/flow/environment.js
@@ -16,6 +16,14 @@ declare var __REACT_DEVTOOLS_GLOBAL_HOOK__: any; /*?{
   inject: ?((stuff: Object) => void)
 };*/
 
+declare var trustedTypes: {|
+  isHTML: (value: any) => boolean,
+  isScript: (value: any) => boolean,
+  isScriptURL: (value: any) => boolean,
+  // TrustedURLs are deprecated and will be removed soon: https://github.com/WICG/trusted-types/pull/204
+  isURL?: (value: any) => boolean,
+|};
+
 // ReactFeatureFlags www fork
 declare module 'ReactFeatureFlags' {
   declare module.exports: any;