diff --git a/Changes b/Changes
index 98c5ce5d72..0262cd8aa4 100644
--- a/Changes
+++ b/Changes
@@ -1,6 +1,13 @@
 10.5.x.x (relative to 10.5.1.0)
 ========
 
+Breaking Changes
+----------------
+- IECoreMaya : Maya meshes converted from Cortex data no longer have normals set explicitly and instead relies on Maya to calculate them.
+
+Fixes
+---
+- ToMayaMeshConverter : No longer locks normals set on the Mesh from the scc.
 
 10.5.1.0 (relative to 10.5.0.0)
 ========
diff --git a/src/IECoreMaya/ToMayaMeshConverter.cpp b/src/IECoreMaya/ToMayaMeshConverter.cpp
index 39fb938e4c..cf31c75187 100644
--- a/src/IECoreMaya/ToMayaMeshConverter.cpp
+++ b/src/IECoreMaya/ToMayaMeshConverter.cpp
@@ -183,6 +183,10 @@ void ToMayaMeshConverter::addUVSet( MFnMesh &fnMesh, const MIntArray &polygonCou
 
 bool ToMayaMeshConverter::doConversion( IECore::ConstObjectPtr from, MObject &to, IECore::ConstCompoundObjectPtr operands ) const
 {
+	// Note: Normals are not set on the Mesh from the scc as by setting them 
+	// explicitly we are implying they should be locked which is not 
+	// supported, instead we rely on Maya computing the normals everytime
+	
 	MStatus s;
 
 	IECoreScene::ConstMeshPrimitivePtr mesh = IECore::runTimeCast<const IECoreScene::MeshPrimitive>( from );
@@ -263,79 +267,6 @@ bool ToMayaMeshConverter::doConversion( IECore::ConstObjectPtr from, MObject &to
 		return false;
 	}
 
-	it = mesh->variables.find("N");
-	if ( it != mesh->variables.end() )
-	{
-		if (it->second.interpolation == IECoreScene::PrimitiveVariable::FaceVarying )
-		{
-			/// \todo Employ some M*Array converters to simplify this
-			MVectorArray vertexNormalsArray;
-			IECore::ConstV3fVectorDataPtr n = IECore::runTimeCast<const IECore::V3fVectorData>(it->second.data);
-			if (n)
-			{
-				IECoreScene::PrimitiveVariable::IndexedView<Imath::V3f> normalView = IECoreScene::PrimitiveVariable::IndexedView<Imath::V3f>( it->second );
-				vertexNormalsArray.setLength( normalView.size() );
-
-				size_t i = 0;
-				for(const auto& normal : normalView)
-				{
-					vertexNormalsArray[i++] = IECore::convert<MVector, Imath::V3f>( normal );
-				}
-			}
-			else
-			{
-				IECore::ConstV3dVectorDataPtr n = IECore::runTimeCast<const IECore::V3dVectorData>(it->second.data);
-				if (n)
-				{
-					IECoreScene::PrimitiveVariable::IndexedView<Imath::V3d> normalView = IECoreScene::PrimitiveVariable::IndexedView<Imath::V3d>( it->second );
-					vertexNormalsArray.setLength( normalView.size() );
-
-					size_t i = 0;
-					for(const auto& normal : normalView)
-					{
-						vertexNormalsArray[i++] = IECore::convert<MVector, Imath::V3d>( normal );
-					}
-				}
-				else
-				{
-					IECore::msg( IECore::Msg::Warning, "ToMayaMeshConverter::doConversion", boost::format( "PrimitiveVariable \"N\" has unsupported type \"%s\"." ) % it->second.data->typeName() );
-				}
-			}
-
-			if ( vertexNormalsArray.length() )
-			{
-				MStatus status;
-				MItMeshPolygon itPolygon( mObj, &status );
-				if( status != MS::kSuccess )
-				{
-					IECore::msg( IECore::Msg::Warning, "ToMayaMeshConverter::doConversion", "Failed to create mesh iterator" );
-				}
-
-				unsigned v = 0;
-				MIntArray vertexIds;
-				MIntArray faceIds;
-
-				for ( ; !itPolygon.isDone(); itPolygon.next() )
-				{
-					for ( v=0; v < itPolygon.polygonVertexCount(); ++v )
-					{
-						faceIds.append( itPolygon.index() );
-						vertexIds.append( itPolygon.vertexIndex( v ) );
-					}
-				}
-
-				if( !fnMesh.setFaceVertexNormals( vertexNormalsArray, faceIds, vertexIds ) )
-				{
-					IECore::msg( IECore::Msg::Warning, "ToMayaMeshConverter::doConversion", "Setting normals failed" );
-				}
-			}
-		}
-		else
-		{
-			IECore::msg( IECore::Msg::Warning, "ToMayaMeshConverter::doConversion", "PrimitiveVariable \"N\" has unsupported interpolation (expected FaceVarying)." );
-		}
-	}
-
 	/// Add UV sets
 	for ( it = mesh->variables.begin(); it != mesh->variables.end(); ++it )
 	{
diff --git a/test/IECoreMaya/ParameterisedHolder.py b/test/IECoreMaya/ParameterisedHolder.py
index c40c4579b8..7fd5b4066e 100644
--- a/test/IECoreMaya/ParameterisedHolder.py
+++ b/test/IECoreMaya/ParameterisedHolder.py
@@ -286,7 +286,6 @@ def testMeshParameterIOProblem( self ) :
 		op = fnOP.getOp()
 
 		mesh = IECoreScene.MeshPrimitive.createBox( imath.Box3f( imath.V3f( -2, -2, -2 ), imath.V3f( 2, 3, 4 ) ) )
-		mesh[ "N" ] = IECoreScene.PrimitiveVariable( mesh[ "N" ].interpolation, mesh[ "N" ].expandedData() )
 		op.parameters()[ "input" ].setValue( mesh )
 		fnOP.setNodeValues()
 
@@ -301,7 +300,13 @@ def testMeshParameterIOProblem( self ) :
 		op = fnOP.getOp()
 
 		mesh2 = op.parameters()["input"].getValue()
+
 		self.assertTrue( mesh2.arePrimitiveVariablesValid() )
+		# The ToMayaMeshConverter relies on Maya to calculate the normals
+		# whereas createBox uses indexed normals so we cannot include them
+		# in the comparison otherwise they will never be the same
+		del mesh[ "N" ]
+		del mesh2[ "N" ]
 		self.assertEqual( mesh2, mesh )
 
 	def testOpHolder( self ) :
diff --git a/test/IECoreMaya/ToMayaMeshConverterTest.py b/test/IECoreMaya/ToMayaMeshConverterTest.py
index 245b1f189c..cfb813b217 100644
--- a/test/IECoreMaya/ToMayaMeshConverterTest.py
+++ b/test/IECoreMaya/ToMayaMeshConverterTest.py
@@ -308,6 +308,9 @@ def testNormals( self ) :
 				self.assertAlmostEqual( origNormal[j], normal3f[j], 6 )
 				self.assertAlmostEqual( origNormal[j], normal3d[j], 6 )
 
+		# normals should always be unlocked when reading from scc
+		self.assertFalse( any( maya.cmds.polyNormalPerVertex( newSphere+".vtx[*]", query=True, allLocked=True ) ) )
+
 	def testSetMeshInterpolation( self ) :
 
 		sphere = maya.cmds.polySphere( subdivisionsX=10, subdivisionsY=5, constructionHistory=False )