diff --git a/docs/api/en/math/Plane.html b/docs/api/en/math/Plane.html
index 5d49db19815c85..1f0be6ae60d5cb 100644
--- a/docs/api/en/math/Plane.html
+++ b/docs/api/en/math/Plane.html
@@ -79,7 +79,7 @@ <h3>[method:Vector3 intersectLine]( [param:Line3 line], [param:Vector3 target] )
 		[page:Line3 line] - the [page:Line3] to check for intersection.<br />
 		[page:Vector3 target] — the result will be copied into this Vector3.<br /><br />
 
-		Returns the intersection point of the passed line and the plane. Returns undefined
+		Returns the intersection point of the passed line and the plane. Returns null
 		 if the line does not intersect. Returns the line's starting point if the line is
 		 coplanar with the plane.
 		</p>
diff --git a/docs/api/zh/math/Plane.html b/docs/api/zh/math/Plane.html
index 8978483dff7f84..667e5a3792da98 100644
--- a/docs/api/zh/math/Plane.html
+++ b/docs/api/zh/math/Plane.html
@@ -75,7 +75,7 @@ <h3>[method:Vector3 intersectLine]( [param:Line3 line], [param:Vector3 target] )
 		[page:Line3 line] - 检测是否相交的三维几何线段 [page:Line3]。<br />
 		[page:Vector3 target] — 结果将会写入该向量中。<br /><br />
 
-		返回给定线段和平面的交点。如果不相交则返回undefined。如果线与平面共面，则返回该线段的起始点。
+		返回给定线段和平面的交点。如果不相交则返回null。如果线与平面共面，则返回该线段的起始点。
 		</p>
 
 		<h3>[method:Boolean intersectsBox]( [param:Box3 box] )</h3>
diff --git a/examples/js/misc/ConvexObjectBreaker.js b/examples/js/misc/ConvexObjectBreaker.js
index 0d15c3c6a9240d..b4642e9bd51e90 100644
--- a/examples/js/misc/ConvexObjectBreaker.js
+++ b/examples/js/misc/ConvexObjectBreaker.js
@@ -347,7 +347,7 @@ THREE.ConvexObjectBreaker.prototype = {
 					var intersection = new THREE.Vector3();
 					intersection = localPlane.intersectLine( this.tempLine1, intersection );
 
-					if ( intersection === undefined ) {
+					if ( intersection === null ) {
 
 						// Shouldn't happen
 						console.error( 'Internal error: segment does not intersect plane.' );
diff --git a/examples/jsm/misc/ConvexObjectBreaker.js b/examples/jsm/misc/ConvexObjectBreaker.js
index 0ab4a3399ec785..1acdfb0bcbf246 100644
--- a/examples/jsm/misc/ConvexObjectBreaker.js
+++ b/examples/jsm/misc/ConvexObjectBreaker.js
@@ -355,7 +355,7 @@ ConvexObjectBreaker.prototype = {
 					var intersection = new Vector3();
 					intersection = localPlane.intersectLine( this.tempLine1, intersection );
 
-					if ( intersection === undefined ) {
+					if ( intersection === null ) {
 
 						// Shouldn't happen
 						console.error( 'Internal error: segment does not intersect plane.' );
diff --git a/src/math/Plane.js b/src/math/Plane.js
index f1e8875c009352..e453512d770fa1 100644
--- a/src/math/Plane.js
+++ b/src/math/Plane.js
@@ -133,7 +133,7 @@ class Plane {
 			}
 
 			// Unsure if this is the correct method to handle this case.
-			return undefined;
+			return null;
 
 		}
 
@@ -141,7 +141,7 @@ class Plane {
 
 		if ( t < 0 || t > 1 ) {
 
-			return undefined;
+			return null;
 
 		}