diff --git a/packages/react-dom/src/client/ReactDOMLegacy.js b/packages/react-dom/src/client/ReactDOMLegacy.js
index 519a0be3bb551..3479e26321ac1 100644
--- a/packages/react-dom/src/client/ReactDOMLegacy.js
+++ b/packages/react-dom/src/client/ReactDOMLegacy.js
@@ -22,6 +22,7 @@ import {
   DOCUMENT_NODE,
   ELEMENT_NODE,
   COMMENT_NODE,
+  DOCUMENT_FRAGMENT_NODE,
 } from '../shared/HTMLNodeType';
 
 import {
@@ -222,7 +223,7 @@ function legacyRenderSubtreeIntoContainer(
 }
 
 export function findDOMNode(
-  componentOrElement: Element | ?React$Component<any, any>,
+  componentOrElement: Element | DocumentFragment | ?React$Component<any, any>,
 ): null | Element | Text {
   if (__DEV__) {
     let owner = (ReactCurrentOwner.current: any);
@@ -244,7 +245,8 @@ export function findDOMNode(
   if (componentOrElement == null) {
     return null;
   }
-  if ((componentOrElement: any).nodeType === ELEMENT_NODE) {
+  const nodeType = (componentOrElement: any).nodeType;
+  if (nodeType === ELEMENT_NODE || nodeType === DOCUMENT_FRAGMENT_NODE) {
     return (componentOrElement: any);
   }
   if (__DEV__) {