diff --git a/src/ifcgeom/IfcGeomRepresentation.h b/src/ifcgeom/IfcGeomRepresentation.h
index 0ca0717e1f..b20c646cf3 100644
--- a/src/ifcgeom/IfcGeomRepresentation.h
+++ b/src/ifcgeom/IfcGeomRepresentation.h
@@ -117,6 +117,7 @@ namespace IfcGeom {
             std::vector<P> uvs_;
 			std::vector<int> _material_ids;
 			std::vector<Material> _materials;
+			size_t weld_offset_;
 			VertexKeyMap welds;
 
 		public:
@@ -130,10 +131,15 @@ namespace IfcGeom {
 			const std::vector<Material>& materials() const { return _materials; }
 
 			Triangulation(const BRep& shape_model)
-					: Representation(shape_model.settings())
-					, id_(shape_model.id())
+				: Representation(shape_model.settings())
+				, id_(shape_model.id())
+				, weld_offset_(0)
 			{
 				for ( IfcGeom::IfcRepresentationShapeItems::const_iterator iit = shape_model.begin(); iit != shape_model.end(); ++ iit ) {
+					
+					// Don't weld vertices that belong to different items to prevent non-manifold situations.
+					weld_offset_ += welds.size();
+					welds.clear();
 
 					int surface_style_id = -1;
 					if (iit->hasStyle()) {
@@ -386,7 +392,7 @@ namespace IfcGeom {
 					const VertexKey key = std::make_pair(material_index, std::make_pair(X, std::make_pair(Y, Z)));
 					typename VertexKeyMap::const_iterator it = welds.find(key);
 					if ( it != welds.end() ) return it->second;
-					i = (int) welds.size();
+					i = (int) welds.size() + weld_offset_;
 					welds[key] = i;
 				}
 				_verts.push_back(X);