diff --git a/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js b/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js
index 3e8af9cb29392..165ce776fb713 100644
--- a/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMHydrationDiff-test.js
@@ -259,7 +259,12 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <main> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\" style=\\"opacity:1\\">
+          +   <main className=\\"only\\" style={{\\"opacity\\":1}} /> <-- client
+
+            </div>
               in main (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -283,7 +288,13 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <header> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+          -   <main class=\\"2\\" /> <-- server
+          +   <header className=\\"1\\" /> <-- client
+              ...
+            </div>
               in header (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -307,7 +318,14 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <main> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+              <header class=\\"1\\" />
+          -   <footer class=\\"3\\" /> <-- server
+          +   <main className=\\"2\\" /> <-- client
+              ...
+            </div>
               in main (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -331,7 +349,14 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <footer> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+              ...
+              <main class=\\"2\\" />
+          +   <footer className=\\"3\\" /> <-- client
+
+            </div>
               in footer (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -354,7 +379,13 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <footer> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+              one
+          +   <footer className=\\"2\\" /> <-- client
+
+            </div>
               in footer (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -505,7 +536,7 @@ describe('ReactDOMServerHydration', () => {
       });
 
       // @gate __DEV__
-      fit('warns when server renders an extra element in the beginning', () => {
+      it('warns when server renders an extra element in the beginning', () => {
         function Mismatch({isClient}) {
           return (
             <div className="parent">
@@ -517,7 +548,13 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <main> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+          -   <header class=\\"1\\" /> <-- server
+          +   <main className=\\"2\\" /> <-- client
+              ...
+            </div>
               in main (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -542,7 +579,14 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <footer> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+              <header class=\\"1\\" />
+          -   <main class=\\"2\\" /> <-- server
+          +   <footer className=\\"3\\" /> <-- client
+              ...
+            </div>
               in footer (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -645,7 +689,13 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <main> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+          -   first <-- server
+          +   <main className=\\"2\\" /> <-- client
+              ...
+            </div>
               in main (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -670,7 +720,14 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <footer> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+              <header class=\\"1\\" />
+          -   second <-- server
+          +   <footer className=\\"3\\" /> <-- client
+              ...
+            </div>
               in footer (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -866,7 +923,14 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <main> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+              <header class=\\"1\\" />
+          -   <footer class=\\"3\\" /> <-- server
+          +   <main className=\\"second\\" /> <-- client
+              ...
+            </div>
               in main (at **)
               in Suspense (at **)
               in div (at **)
@@ -892,7 +956,14 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <footer> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+              <header class=\\"1\\" />
+          -   <main class=\\"second\\" /> <-- server
+          +   <footer className=\\"3\\" /> <-- client
+              ...
+            </div>
               in footer (at **)
               in Suspense (at **)
               in div (at **)
@@ -966,7 +1037,12 @@ describe('ReactDOMServerHydration', () => {
         }
         expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
           Array [
-            "Warning: Expected server HTML to contain a matching <header> in <div>.
+            "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+            <div class=\\"parent\\">
+          +   <header className=\\"1\\" /> <-- client
+
+            </div>
               in header (at **)
               in div (at **)
               in Mismatch (at **)",
@@ -1050,7 +1126,14 @@ describe('ReactDOMServerHydration', () => {
 
       expect(testMismatch(Mismatch)).toMatchInlineSnapshot(`
         Array [
-          "Warning: Expected server HTML to contain a matching <footer> in <div>.
+          "Warning: The content rendered by the server and the client did not match because the client has rendered an extra element. The mismatch occurred inside of this parent:
+
+          <div class=\\"parent\\">
+            ...
+            <main class=\\"2\\" />
+        +   <footer className=\\"3\\" /> <-- client
+
+          </div>
             in footer (at **)
             in Panel (at **)
             in div (at **)
diff --git a/packages/react-dom/src/client/ReactDOMComponent.js b/packages/react-dom/src/client/ReactDOMComponent.js
index ea2068902c3e3..a9772152f4b24 100644
--- a/packages/react-dom/src/client/ReactDOMComponent.js
+++ b/packages/react-dom/src/client/ReactDOMComponent.js
@@ -1351,25 +1351,28 @@ function formatDiffForExtraServerNode(parentNode, child) {
 function formatDiffForExtraClientNode(parentNode, tag, props, mismatchNode) {
   let formattedSibling = null;
   let prevSibling = null;
-  if (mismatchNode !== null) {
+  if (mismatchNode != null) {
     prevSibling = findPreviousSiblingForDiff(mismatchNode);
   } else if (parentNode.lastChild !== null) {
     prevSibling = parentNode.lastChild;
   }
+  let formattedChildren = '';
   if (prevSibling !== null) {
     formattedSibling = formatNode(prevSibling, '    ');
-  }
-  let formattedChildren = '';
-  if (formattedSibling !== null) {
-    if (findPreviousSiblingForDiff(prevSibling) !== null) {
-      formattedChildren += '    ...\n';
+    if (formattedSibling !== null) {
+      if (findPreviousSiblingForDiff(prevSibling) !== null) {
+        formattedChildren += '    ...\n';
+      }
+      formattedChildren += formattedSibling + '\n';
     }
-    formattedChildren += formattedSibling + '\n';
+  }
+  if (mismatchNode != null) {
+    formattedChildren += formatNode(mismatchNode, '-   ') + ' <-- server\n';
   }
   formattedChildren += formatReactElement(tag, props, '+   ');
-  formattedChildren += ' <-- client';
-  if (mismatchNode !== null) {
-    formattedChildren += '\n    ...';
+  formattedChildren += ' <-- client\n';
+  if (mismatchNode != null) {
+    formattedChildren += '    ...';
   }
   return formatElement(parentNode, '  ', formattedChildren);
 }
diff --git a/packages/react-reconciler/src/ReactFiberHydrationContext.new.js b/packages/react-reconciler/src/ReactFiberHydrationContext.new.js
index 64cbd2173b176..b8c7b94ea77fe 100644
--- a/packages/react-reconciler/src/ReactFiberHydrationContext.new.js
+++ b/packages/react-reconciler/src/ReactFiberHydrationContext.new.js
@@ -324,7 +324,7 @@ function insertNonHydratedInstance(
   mismatchInstance,
 ) {
   fiber.flags = (fiber.flags & ~Hydrating) | Placement;
-  warnNonhydratedInstance(returnFiber, fiber, lastHydratedChild);
+  warnNonhydratedInstance(returnFiber, fiber, mismatchInstance);
 }
 
 function tryHydrate(fiber, nextInstance) {