diff --git a/src/ifcgeom/mapping/IfcSectionedSolidHorizontal.cpp b/src/ifcgeom/mapping/IfcSectionedSolidHorizontal.cpp
index 14ee9899ad..52187d7e5e 100644
--- a/src/ifcgeom/mapping/IfcSectionedSolidHorizontal.cpp
+++ b/src/ifcgeom/mapping/IfcSectionedSolidHorizontal.cpp
@@ -31,10 +31,10 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcSectionedSolidHorizontal* in
 	std::vector<cross_section> cross_sections;
 
 	auto dir = map(inst->Directrix());
-	auto pwf = taxonomy::dcast<taxonomy::piecewise_function>(dir);
-	if (!pwf) {
+	auto fn = taxonomy::dcast<taxonomy::function_item>(dir);
+	if (!fn) {
 		// Only implement on alignment curves
-        Logger::Warning("IfcSectionedSolidHorizontal is only implemented for piecewise function Directrix curves", inst);
+        Logger::Warning("IfcSectionedSolidHorizontal is only implemented for Directrix curves based on taxonomy::function_item", inst);
         return nullptr;
 	}
 
@@ -70,9 +70,6 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcSectionedSolidHorizontal* in
 
 		profile_offsets.push_back(po);
 	}
-#else
-	return nullptr;
-#endif
 	if (faces.size() != profile_offsets.size()) {
 		Logger::Warning("Expected CrossSections and CrossSectionPositions to be equal length, but got " + std::to_string(faces.size()) + " and " + std::to_string(profile_offsets.size()) + " respectively", inst);
 		return nullptr;
@@ -85,9 +82,12 @@ taxonomy::ptr mapping::map_impl(const IfcSchema::IfcSectionedSolidHorizontal* in
 	for (size_t i = 0; i < faces.size(); ++i) {
 		cross_sections.push_back({ longitudes[i], faces[i], profile_offsets[i] });
 	}
-	}
+#else
+    return nullptr;
+#endif
+   }
 
-	return make_loft(settings_, inst, pwf, cross_sections);
+	return make_loft(settings_, inst, fn, cross_sections);
 }
 
 #endif
diff --git a/src/ifcgeom/taxonomy.cpp b/src/ifcgeom/taxonomy.cpp
index b2d48478f3..6fc7288dda 100644
--- a/src/ifcgeom/taxonomy.cpp
+++ b/src/ifcgeom/taxonomy.cpp
@@ -800,13 +800,14 @@ boost::optional<face::ptr> ifcopenshell::geometry::taxonomy::curve_to_face_upgra
 }
 
 
-boost::optional<piecewise_function::ptr> ifcopenshell::geometry::taxonomy::loop_to_piecewise_function_upgrade_impl(ptr item) {
-	boost::optional<piecewise_function::ptr> pwf_;
+boost::optional<function_item::ptr> ifcopenshell::geometry::taxonomy::loop_to_function_item_upgrade_impl(ptr item) {
+	boost::optional<function_item::ptr> fi_;
 	auto loop_ = dcast<loop>(item);
 	if (loop_) {
-		if (loop_->pwf.is_initialized()) {
-			pwf_ = loop_->pwf;
+		if (loop_->fi.is_initialized()) {
+			fi_ = loop_->fi;
 		} else {
+         // piecewise_function is a specialization of function_item - callers don't need to know this detail
 			piecewise_function::spans_t spans;
 			spans.reserve(loop_->children.size());
 			for (auto& edge_ : loop_->children) {
@@ -828,9 +829,9 @@ boost::optional<piecewise_function::ptr> ifcopenshell::geometry::taxonomy::loop_
 				};
             spans.emplace_back(taxonomy::make<taxonomy::functor_item>(l, fn));
 			}
-			pwf_ = make<piecewise_function>(0.0,spans);
-			loop_->pwf = pwf_;
+			fi_ = make<piecewise_function>(0.0,spans);
+			loop_->fi = fi_;
 		}
 	}
-	return pwf_;
+    return fi_;
 }
diff --git a/src/ifcgeom/taxonomy.h b/src/ifcgeom/taxonomy.h
index 4f73f10a66..703504abc2 100644
--- a/src/ifcgeom/taxonomy.h
+++ b/src/ifcgeom/taxonomy.h
@@ -892,7 +892,7 @@ typedef item const* ptr;
 				DECLARE_PTR(loop)
 
 				boost::optional<bool> external, closed;
-				boost::optional<taxonomy::piecewise_function::ptr> pwf;
+				boost::optional<taxonomy::function_item::ptr> fi;
 
 				bool is_polyhedron() const {
 					for (auto& e : children) {
@@ -1374,27 +1374,27 @@ typedef item const* ptr;
 				}
 			};
 
-			boost::optional<piecewise_function::ptr> loop_to_piecewise_function_upgrade_impl(ptr item);
+			boost::optional<function_item::ptr> loop_to_function_item_upgrade_impl(ptr item);
             template <typename T>
-            class loop_to_piecewise_function_upgrade {
+            class loop_to_function_item_upgrade {
               private:
-                boost::optional<taxonomy::piecewise_function::ptr> pwf_;
+                boost::optional<taxonomy::function_item::ptr> fi_;
 
               public:
-               loop_to_piecewise_function_upgrade(taxonomy::ptr item) {
-					if constexpr (std::is_same_v<T, piecewise_function>) {
-						pwf_ = loop_to_piecewise_function_upgrade_impl(item);
+               loop_to_function_item_upgrade(taxonomy::ptr item) {
+					if constexpr (std::is_same_v<T, function_item>) {
+						fi_ = loop_to_function_item_upgrade_impl(item);
                     }
                 }
 
                 operator bool() const {
-                    return pwf_.is_initialized();
+                    return fi_.is_initialized();
                 }
 
                 operator typename T::ptr() const {
-					if constexpr (std::is_same_v<T, piecewise_function>) {
-						if (pwf_) {
-							return *pwf_;
+					if constexpr (std::is_same_v<T, function_item>) {
+						if (fi_) {
+							return *fi_;
 						}
 					}
 					return nullptr;
@@ -1435,7 +1435,7 @@ typedef item const* ptr;
 					}
 				}
 				{
-					loop_to_piecewise_function_upgrade<T> upg(u);
+					loop_to_function_item_upgrade<T> upg(u);
 					if (upg) {
 						return upg;
 					}
@@ -1479,7 +1479,7 @@ typedef item const* ptr;
 					}
 				}
 				{
-					loop_to_piecewise_function_upgrade<T> upg(u);
+					loop_to_function_item_upgrade<T> upg(u);
 					if (upg) {
 						return upg;
 					}
diff --git a/src/ifcwrap/IfcPython.i b/src/ifcwrap/IfcPython.i
index b6f344da1a..ec726fb5f2 100644
--- a/src/ifcwrap/IfcPython.i
+++ b/src/ifcwrap/IfcPython.i
@@ -86,7 +86,7 @@
 %ignore curve_to_loop_upgrade_impl;
 %ignore edge_to_loop_upgrade_impl;
 %ignore curve_to_face_upgrade_impl;
-%ignore loop_to_piecewise_function_upgrade_impl;
+%ignore loop_to_function_item_upgrade_impl;
 
 // settings, can this done more generally?
 %ignore UseElementNames;