diff --git a/manual/pages/installation.html b/manual/pages/installation.html
index 558bb8b9466959..af6fc7a59e47f2 100644
--- a/manual/pages/installation.html
+++ b/manual/pages/installation.html
@@ -253,7 +253,7 @@ <h3>Production</h3>
             <i><b>IMPORTANT:</b> Import all dependencies from the same version of three.js, and from the same CDN. Mixing files from different sources may cause duplicate code to be included, or even break the application in unexpected ways.</i>
           </p>
 
-          <h2>Addons</h2>
+          <h2 id="addons">Addons</h2>
 
           <p>
             Out of the box, three.js includes the fundamentals of a 3D engine. Other three.js components — such as controls, loaders, and post-processing effects — are part of the [link:https://github.com/mrdoob/three.js/tree/dev/examples/jsm addons/] directory. Addons do not need to be <i>installed</i> separately, but do need to be <i>imported</i> separately.
diff --git a/src/math/Ray.js b/src/math/Ray.js
index 8edd1a7497e6fd..94391ddd4482aa 100644
--- a/src/math/Ray.js
+++ b/src/math/Ray.js
@@ -306,6 +306,8 @@ class Ray {
 	 */
 	intersectSphere( sphere, target ) {
 
+		if ( sphere.radius < 0 ) return null; // handle empty spheres, see #31187
+
 		_vector.subVectors( sphere.center, this.origin );
 		const tca = _vector.dot( this.direction );
 		const d2 = _vector.dot( _vector ) - tca * tca;
diff --git a/test/unit/src/math/Ray.tests.js b/test/unit/src/math/Ray.tests.js
index 0a956ef71c56be..0dad45816f774a 100644
--- a/test/unit/src/math/Ray.tests.js
+++ b/test/unit/src/math/Ray.tests.js
@@ -260,6 +260,13 @@ export default QUnit.module( 'Maths', () => {
 			a0.intersectSphere( b, point );
 			assert.ok( point.distanceTo( new Vector3( 0, 0, - 5 ) ) < TOL, 'Passed!' );
 
+			// empty sphere ( negative radius ) can never be intersected, so the
+			// target must be left untouched and the return value must be null,
+			// consistent with intersectsSphere()
+			b = new Sphere( new Vector3( 0, 0, - 1 ), - 1 );
+			assert.strictEqual( a0.intersectSphere( b, point.copy( posInf3 ) ), null, 'Passed!' );
+			assert.ok( point.equals( posInf3 ), 'Passed!' );
+
 		} );
 
 		QUnit.test( 'intersectsSphere', ( assert ) => {
diff --git a/utils/docs/template/tmpl/container.tmpl b/utils/docs/template/tmpl/container.tmpl
index ba51458c7e1e60..c95d2c87559b49 100644
--- a/utils/docs/template/tmpl/container.tmpl
+++ b/utils/docs/template/tmpl/container.tmpl
@@ -42,7 +42,7 @@
 			<article>
 				<?js if (doc.import) { ?>
 				<h2 class="subsection-title">Import</h2>
-				<p><span translate="no"><?js= doc.name ?></span> is an addon, and must be imported explicitly, see <a href="https://threejs.org/manual/#installation">Installation#Addons</a>.</p>
+				<p><span translate="no"><?js= doc.name ?></span> is an addon, and must be imported explicitly, see <a href="https://threejs.org/manual/#installation#addons">Installation#Addons</a>.</p>
 				<pre class="prettyprint source lang-js" translate="no"><code><?js= doc.import ?></code></pre>
 				<?js } ?>
 				<div class="container-overview">