diff --git a/src/ifcgeom/AbstractKernel.h b/src/ifcgeom/AbstractKernel.h
index ed4985c056..c78794c862 100644
--- a/src/ifcgeom/AbstractKernel.h
+++ b/src/ifcgeom/AbstractKernel.h
@@ -111,7 +111,7 @@ namespace {
 	/* A compile-time for loop over the taxonomy kinds */
 	template <size_t N>
 	struct dispatch_conversion {
-		static bool dispatch(ifcopenshell::geometry::kernels::AbstractKernel* kernel, ifcopenshell::geometry::taxonomy::kinds item_kind, const ifcopenshell::geometry::taxonomy::ptr item, IfcGeom::ConversionResults& results) {
+		static bool dispatch(ifcopenshell::geometry::kernels::AbstractKernel* kernel, ifcopenshell::geometry::taxonomy::kinds item_kind, const ifcopenshell::geometry::taxonomy::ptr& item, IfcGeom::ConversionResults& results) {
 			if (N == item_kind) {
 				auto concrete_item = std::static_pointer_cast<ifcopenshell::geometry::taxonomy::type_by_kind::type<N>>(item);
 				return kernel->convert_impl(concrete_item, results);
@@ -123,7 +123,7 @@ namespace {
 
 	template <>
 	struct dispatch_conversion<ifcopenshell::geometry::taxonomy::type_by_kind::max> {
-		static bool dispatch(ifcopenshell::geometry::kernels::AbstractKernel*, ifcopenshell::geometry::taxonomy::kinds, const ifcopenshell::geometry::taxonomy::ptr item, IfcGeom::ConversionResults&) {
+		static bool dispatch(ifcopenshell::geometry::kernels::AbstractKernel*, ifcopenshell::geometry::taxonomy::kinds, const ifcopenshell::geometry::taxonomy::ptr& item, IfcGeom::ConversionResults&) {
 			Logger::Error("No conversion for " + std::to_string(item->kind()));
 			return false;
 		}
@@ -131,7 +131,7 @@ namespace {
 
 	template <size_t N>
 	struct dispatch_with_upgrade {
-		static bool dispatch(ifcopenshell::geometry::kernels::AbstractKernel* kernel, const ifcopenshell::geometry::taxonomy::ptr item, IfcGeom::ConversionResults& results) {
+		static bool dispatch(ifcopenshell::geometry::kernels::AbstractKernel* kernel, const ifcopenshell::geometry::taxonomy::ptr& item, IfcGeom::ConversionResults& results) {
 			auto concrete_item = ifcopenshell::geometry::taxonomy::template dcast<ifcopenshell::geometry::taxonomy::upgrades::type<N>>(item);
 			if (concrete_item) {
 				return kernel->convert_impl(concrete_item, results);
@@ -143,7 +143,7 @@ namespace {
 
 	template <>
 	struct dispatch_with_upgrade<ifcopenshell::geometry::taxonomy::upgrades::max> {
-		static bool dispatch(ifcopenshell::geometry::kernels::AbstractKernel*, const ifcopenshell::geometry::taxonomy::ptr item, IfcGeom::ConversionResults&) {
+		static bool dispatch(ifcopenshell::geometry::kernels::AbstractKernel*, const ifcopenshell::geometry::taxonomy::ptr& item, IfcGeom::ConversionResults&) {
 			Logger::Error("No conversion with upgrade for " + std::to_string(item->kind()));
 			return false;
 		}
@@ -165,7 +165,7 @@ namespace {
 	/* A compile-time for loop over the curve kinds */
 	template <typename T, size_t N = 0>
 	struct dispatch_curve_creation {
-		static bool dispatch(const ifcopenshell::geometry::taxonomy::ptr item, T& visitor) {
+		static bool dispatch(const ifcopenshell::geometry::taxonomy::ptr& item, T& visitor) {
 			constexpr auto KindIndex = TupleTypeIndex<std::tuple_element_t<N, ifcopenshell::geometry::taxonomy::impl::CurvesTuple>, ifcopenshell::geometry::taxonomy::impl::KindsTuple>::value;
 			if (item->kind() == KindIndex) {
 				auto concrete_item = std::static_pointer_cast<ifcopenshell::geometry::taxonomy::curves::type<N>>(item);
@@ -179,7 +179,7 @@ namespace {
 
 	template <typename T>
 	struct dispatch_curve_creation<T, ifcopenshell::geometry::taxonomy::curves::max> {
-		static bool dispatch(const ifcopenshell::geometry::taxonomy::ptr item, T&) {
+		static bool dispatch(const ifcopenshell::geometry::taxonomy::ptr& item, T&) {
 			Logger::Error("No conversion for " + std::to_string(item->kind()));
 			return false;
 		}
@@ -188,7 +188,7 @@ namespace {
 	/* A compile-time for loop over the curve kinds */
 	template <typename T, size_t N = 0>
 	struct dispatch_surface_creation {
-		static bool dispatch(const ifcopenshell::geometry::taxonomy::ptr item, T& visitor) {
+		static bool dispatch(const ifcopenshell::geometry::taxonomy::ptr& item, T& visitor) {
 			auto v = ifcopenshell::geometry::taxonomy::template dcast<ifcopenshell::geometry::taxonomy::surfaces::type<N>>(item);
 			if (v && item->kind() == v->kind()) {
 				visitor(v);
@@ -201,7 +201,7 @@ namespace {
 
 	template <typename T>
 	struct dispatch_surface_creation<T, ifcopenshell::geometry::taxonomy::surfaces::max> {
-		static bool dispatch(const ifcopenshell::geometry::taxonomy::ptr item, T&) {
+		static bool dispatch(const ifcopenshell::geometry::taxonomy::ptr& item, T&) {
 			Logger::Error("No conversion for " + std::to_string(item->kind()));
 			return false;
 		}