diff --git a/src/constants.js b/src/constants.js
index 7a823a3efd..1ad82b208e 100644
--- a/src/constants.js
+++ b/src/constants.js
@@ -31,3 +31,5 @@ export const NULL = null;
 export const UNDEFINED = undefined;
 export const EMPTY_OBJ = /** @type {any} */ ({});
 export const EMPTY_ARR = [];
+
+export const MATHML_TOKEN_ELEMENTS = /(mi|mn|mo|ms$|mte|msp)/;
diff --git a/src/diff/index.js b/src/diff/index.js
index 73c4a01ebb..427d3cf314 100644
--- a/src/diff/index.js
+++ b/src/diff/index.js
@@ -12,7 +12,8 @@ import {
 	RESET_MODE,
 	SVG_NAMESPACE,
 	UNDEFINED,
-	XHTML_NAMESPACE
+	XHTML_NAMESPACE,
+	MATHML_TOKEN_ELEMENTS
 } from '../constants';
 import { BaseComponent, getDomSibling } from '../component';
 import { Fragment } from '../create-element';
@@ -608,6 +609,13 @@ function diffElementNodes(
 		} else {
 			if (oldHtml) dom.innerHTML = '';
 
+			if (
+				nodeType == 'foreignObject' ||
+				(namespace == MATH_NAMESPACE && MATHML_TOKEN_ELEMENTS.test(nodeType))
+			) {
+				namespace = XHTML_NAMESPACE;
+			}
+
 			diffChildren(
 				// @ts-expect-error
 				nodeType == 'template' ? dom.content : dom,
@@ -615,7 +623,7 @@ function diffElementNodes(
 				newVNode,
 				oldVNode,
 				globalContext,
-				nodeType == 'foreignObject' ? XHTML_NAMESPACE : namespace,
+				namespace,
 				excessDomChildren,
 				commitQueue,
 				excessDomChildren
diff --git a/test/browser/mathml.test.jsx b/test/browser/mathml.test.jsx
index 79439f4016..0f5f43023e 100644
--- a/test/browser/mathml.test.jsx
+++ b/test/browser/mathml.test.jsx
@@ -2,6 +2,9 @@ import { createElement, Component, render } from 'preact';
 import { setupRerender } from 'preact/test-utils';
 import { setupScratch, teardown } from '../_util/helpers';
 
+const XHTML_NAMESPACE = 'http://www.w3.org/1999/xhtml';
+const MATH_NAMESPACE = 'http://www.w3.org/1998/Math/MathML';
+
 describe('mathml', () => {
 	let scratch;
 
@@ -18,7 +21,7 @@ describe('mathml', () => {
 
 		let namespace = scratch.querySelector('math').namespaceURI;
 
-		expect(namespace).to.equal('http://www.w3.org/1998/Math/MathML');
+		expect(namespace).to.equal(MATH_NAMESPACE);
 	});
 
 	it('should render children with the correct namespace URI', () => {
@@ -31,12 +34,12 @@ describe('mathml', () => {
 
 		let namespace = scratch.querySelector('mrow').namespaceURI;
 
-		expect(namespace).to.equal('http://www.w3.org/1998/Math/MathML');
+		expect(namespace).to.equal(MATH_NAMESPACE);
 	});
 
 	it('should inherit correct namespace URI from parent', () => {
 		const math = document.createElementNS(
-			'http://www.w3.org/1998/Math/MathML',
+			MATH_NAMESPACE,
 			'math'
 		);
 		scratch.appendChild(math);
@@ -44,14 +47,14 @@ describe('mathml', () => {
 		render(<mrow />, scratch.firstChild);
 
 		let namespace = scratch.querySelector('mrow').namespaceURI;
-		expect(namespace).to.equal('http://www.w3.org/1998/Math/MathML');
+		expect(namespace).to.equal(MATH_NAMESPACE);
 	});
 
 	it('should inherit correct namespace URI from parent upon updating', () => {
 		setupRerender();
 
 		const math = document.createElementNS(
-			'http://www.w3.org/1998/Math/MathML',
+			MATH_NAMESPACE,
 			'math'
 		);
 		scratch.appendChild(math);
@@ -62,7 +65,7 @@ describe('mathml', () => {
 				// eslint-disable-next-line
 				this.setState({ show: false }, () => {
 					expect(scratch.querySelector('mo').namespaceURI).to.equal(
-						'http://www.w3.org/1998/Math/MathML'
+						MATH_NAMESPACE
 					);
 				});
 			}
@@ -90,4 +93,24 @@ describe('mathml', () => {
 		expect(scratch.firstChild).to.be.an('HTMLDivElement');
 		expect(scratch.firstChild.firstChild).to.be.an('MathMLElement');
 	});
+
+	it('should support XHTML phrasing content within MathML token elements', () => {
+		render(
+			<div>
+				<math>
+					<mrow>
+						<mi><ins>123</ins></mi>
+					</mrow>
+				</math>
+			</div>,
+			scratch
+		);
+
+		expect(scratch.querySelector('mi').namespaceURI).to.equal(
+			MATH_NAMESPACE
+		);
+		expect(scratch.querySelector('ins').namespaceURI).to.equal(
+			XHTML_NAMESPACE
+		);
+	});
 });