diff --git a/src/renderers/shaders/ShaderChunk/defaultnormal_vertex.glsl.js b/src/renderers/shaders/ShaderChunk/defaultnormal_vertex.glsl.js
index 1dc9bf56744ad7..0c1e1301561c9f 100644
--- a/src/renderers/shaders/ShaderChunk/defaultnormal_vertex.glsl.js
+++ b/src/renderers/shaders/ShaderChunk/defaultnormal_vertex.glsl.js
@@ -53,11 +53,5 @@ transformedNormal = normalMatrix * transformedNormal;
 
 	transformedTangent = ( modelViewMatrix * vec4( transformedTangent, 0.0 ) ).xyz;
 
-	#ifdef FLIP_SIDED
-
-		transformedTangent = - transformedTangent;
-
-	#endif
-
 #endif
 `;
diff --git a/src/renderers/shaders/ShaderChunk/normal_fragment_begin.glsl.js b/src/renderers/shaders/ShaderChunk/normal_fragment_begin.glsl.js
index 6d661270f036ae..fbe698922ba8fc 100644
--- a/src/renderers/shaders/ShaderChunk/normal_fragment_begin.glsl.js
+++ b/src/renderers/shaders/ShaderChunk/normal_fragment_begin.glsl.js
@@ -39,7 +39,7 @@ float faceDirection = gl_FrontFacing ? 1.0 : - 1.0;
 
 	#endif
 
-	#if defined( DOUBLE_SIDED ) && ! defined( FLAT_SHADED )
+	#ifdef DOUBLE_SIDED
 
 		tbn[0] *= faceDirection;
 		tbn[1] *= faceDirection;
@@ -60,7 +60,7 @@ float faceDirection = gl_FrontFacing ? 1.0 : - 1.0;
 
 	#endif
 
-	#if defined( DOUBLE_SIDED ) && ! defined( FLAT_SHADED )
+	#ifdef DOUBLE_SIDED
 
 		tbn2[0] *= faceDirection;
 		tbn2[1] *= faceDirection;
diff --git a/src/renderers/shaders/ShaderChunk/normal_vertex.glsl.js b/src/renderers/shaders/ShaderChunk/normal_vertex.glsl.js
index 4b93b94eedb9dc..34bafed06db3d8 100644
--- a/src/renderers/shaders/ShaderChunk/normal_vertex.glsl.js
+++ b/src/renderers/shaders/ShaderChunk/normal_vertex.glsl.js
@@ -8,6 +8,12 @@ export default /* glsl */`
 		vTangent = normalize( transformedTangent );
 		vBitangent = normalize( cross( vNormal, vTangent ) * tangent.w );
 
+		#ifdef FLIP_SIDED
+
+			vBitangent = - vBitangent;
+
+		#endif
+
 	#endif
 
 #endif