diff --git a/src/core/TriangleSplitter.js b/src/core/TriangleSplitter.js
index 123cf9e0..d4f15fd8 100644
--- a/src/core/TriangleSplitter.js
+++ b/src/core/TriangleSplitter.js
@@ -112,11 +112,7 @@ export class TriangleSplitter {
 
 		if ( Math.abs( 1.0 - Math.abs( _triangleNormal.dot( normal ) ) ) < PARALLEL_EPSILON ) {
 
-			if ( this.coplanarTriangleUsed === false ) {
-
-				this.coplanarTriangleUsed = true;
-
-			}
+			this.coplanarTriangleUsed = true;
 
 			for ( let i = 0, l = triangles.length; i < l; i ++ ) {
 
diff --git a/src/core/operations/operations.js b/src/core/operations/operations.js
index e97d5fb7..bbf801c2 100644
--- a/src/core/operations/operations.js
+++ b/src/core/operations/operations.js
@@ -10,6 +10,7 @@ import {
 } from './operationsUtils.js';
 import { getTriCount } from '../utils/geometryUtils.js';
 import { HOLLOW_INTERSECTION, HOLLOW_SUBTRACTION } from '../constants.js';
+import { isTriDegenerate } from '../utils/triangleUtils.js';
 
 const _matrix = new Matrix4();
 const _normalMatrix = new Matrix3();
@@ -296,12 +297,19 @@ function performWholeTriangleOperations(
 				const i2 = aIndex.getX( i3 + 2 );
 				const groupIndex = groupOffset === - 1 ? 0 : groupIndices[ currId ] + groupOffset;
 
-				for ( let k = 0, lk = _attr.length; k < lk; k ++ ) {
+				_tri.a.fromBufferAttribute( aPosition, i0 );
+				_tri.b.fromBufferAttribute( aPosition, i1 );
+				_tri.c.fromBufferAttribute( aPosition, i2 );
+				if ( ! isTriDegenerate( _tri ) ) {
 
-					const action = _actions[ k ];
-					const attrSet = _attr[ k ].getGroupAttrSet( groupIndex );
-					const invertTri = action === INVERT_TRI;
-					appendAttributesFromIndices( i0, i1, i2, aAttributes, a.matrixWorld, _normalMatrix, attrSet, invertTri !== invertedGeometry );
+					for ( let k = 0, lk = _attr.length; k < lk; k ++ ) {
+
+						const action = _actions[ k ];
+						const attrSet = _attr[ k ].getGroupAttrSet( groupIndex );
+						const invertTri = action === INVERT_TRI;
+						appendAttributesFromIndices( i0, i1, i2, aAttributes, a.matrixWorld, _normalMatrix, attrSet, invertTri !== invertedGeometry );
+
+					}
 
 				}
 
diff --git a/src/core/utils/triangleUtils.js b/src/core/utils/triangleUtils.js
index 76e1c464..62671acd 100644
--- a/src/core/utils/triangleUtils.js
+++ b/src/core/utils/triangleUtils.js
@@ -10,10 +10,10 @@ export function isTriDegenerate( tri, eps = EPSILON ) {
 	// compute angles to determine whether they're degenerate
 	_AB.subVectors( tri.b, tri.a );
 	_AC.subVectors( tri.c, tri.a );
-	_CB.subVectors( tri.c, tri.b );
+	_CB.subVectors( tri.b, tri.c );
 
 	const angle1 = _AB.angleTo( _AC );				// AB v AC
-	const angle2 = _AB.angleTo( _CB ) - Math.PI;	// AB v BC - 180deg
+	const angle2 = _AB.angleTo( _CB );				// AB v BC
 	const angle3 = Math.PI - angle1 - angle2;		// 180deg - angle1 - angle2
 
 	return Math.abs( angle1 ) < eps ||