diff --git a/src/nodes/accessors/SceneProperties.js b/src/nodes/accessors/SceneProperties.js
index cea87c6968eec1..14e977921d8baf 100644
--- a/src/nodes/accessors/SceneProperties.js
+++ b/src/nodes/accessors/SceneProperties.js
@@ -31,7 +31,7 @@ export const backgroundRotation = /*@__PURE__*/ uniform( new Matrix4() ).setGrou
 
 	const background = scene.background;
 
-	if ( background !== null && background.isTexture && background.mapping !== UVMapping ) {
+	if ( ( background !== null && background.isTexture && background.mapping !== UVMapping ) || ( scene.backgroundNode && scene.backgroundNode.isNode ) ) {
 
 		// note: since the matrix is orthonormal, we can use the more-efficient transpose() in lieu of invert()
 		_m1.makeRotationFromEuler( scene.backgroundRotation ).transpose();
diff --git a/src/nodes/core/MRTNode.js b/src/nodes/core/MRTNode.js
index b6d46ba751ef1f..eaf54b6bcd4f9e 100644
--- a/src/nodes/core/MRTNode.js
+++ b/src/nodes/core/MRTNode.js
@@ -170,6 +170,10 @@ class MRTNode extends OutputStructNode {
 		for ( const name in outputNodes ) {
 
 			const index = getTextureIndex( textures, name );
+
+			// Ignore if the output exists in the MRT but has never been used.
+			if ( index === - 1 ) continue;
+
 			const type = builder.getOutputType( index );
 
 			members[ index ] = outputNodes[ name ].convert( type );