diff --git a/src/ifcgeom/IfcGeomWires.cpp b/src/ifcgeom/IfcGeomWires.cpp
index 6bd664aafe..10390eee28 100644
--- a/src/ifcgeom/IfcGeomWires.cpp
+++ b/src/ifcgeom/IfcGeomWires.cpp
@@ -91,6 +91,10 @@
 #include <TopTools_ListOfShape.hxx>
 #include <TopTools_ListIteratorOfListOfShape.hxx>
 
+#include <BRepAdaptor_CompCurve.hxx>
+#include <BRepAdaptor_HCompCurve.hxx>
+#include <Approx_Curve3d.hxx>
+
 #include "../ifcgeom/IfcGeom.h"
 
 #define Kernel MAKE_TYPE_NAME(Kernel)
@@ -421,7 +425,21 @@ bool IfcGeom::Kernel::convert(const IfcSchema::IfcTrimmedCurve* l, TopoDS_Wire&
 	double parameterFactor = isConic ? getValue(GV_PLANEANGLE_UNIT) : getValue(GV_LENGTH_UNIT);
 	
 	Handle(Geom_Curve) curve;
-	if ( !convert_curve(basis_curve,curve) ) return false;
+	if (shape_type(basis_curve) == ST_CURVE) {
+		if (!convert_curve(basis_curve, curve)) return false;
+	} else if (shape_type(basis_curve) == ST_WIRE) {
+		Logger::Warning("Approximating BasisCurve due to possible discontinuities", l);
+		TopoDS_Wire w;
+		if (!convert_wire(basis_curve, w)) return false;
+		BRepAdaptor_CompCurve cc(w, true);
+		Handle(Adaptor3d_HCurve) hcc = Handle(Adaptor3d_HCurve)(new BRepAdaptor_HCompCurve(cc));
+		// @todo, arbitrary numbers here, note they cannot be too high as contiguous memory is allocated based on them.
+		Approx_Curve3d approx(hcc, getValue(GV_PRECISION), GeomAbs_C0, 10, 10);
+		curve = approx.Curve();
+	} else {
+		Logger::Error("Unknown BasisCurve", l);
+		return false;
+	}
 	
 	bool trim_cartesian = l->MasterRepresentation() != IfcSchema::IfcTrimmingPreference::IfcTrimmingPreference_PARAMETER;
 	IfcEntityList::ptr trims1 = l->Trim1();
diff --git a/src/ifcopenshell-python/ifcopenshell/entity_instance.py b/src/ifcopenshell-python/ifcopenshell/entity_instance.py
index 3586bfa793..7245785e16 100644
--- a/src/ifcopenshell-python/ifcopenshell/entity_instance.py
+++ b/src/ifcopenshell-python/ifcopenshell/entity_instance.py
@@ -108,22 +108,33 @@ class entity_instance(object):
         return entity_instance.wrap_value(self.wrapped_data.get_argument(key))
 
     def __setitem__(self, idx, value):
+        attr_type = real_attr_type = self.attribute_type(idx).title().replace(' ', '')
+        real_attr_type = real_attr_type.replace('Derived', 'None')
+        attr_type = attr_type.replace('Binary', 'String')
+        attr_type = attr_type.replace('Enumeration', 'String')
+        
         if value is None:
-            self.wrapped_data.setArgumentAsNull(idx)
+            if attr_type != "Derived":
+                self.wrapped_data.setArgumentAsNull(idx)
         else:
-            attr_type = real_attr_type = self.attribute_type(idx).title().replace(' ', '')
-            attr_type = attr_type.replace('Binary', 'String')
-            attr_type = attr_type.replace('Enumeration', 'String')
-            try:
-                if isinstance(value, unicode):
-                    value = value.encode("utf-8")
-            except BaseException:
-                pass
-            try:
-                getattr(self.wrapped_data, "setArgumentAs%s" % attr_type)(idx, entity_instance.unwrap_value(value))
-            except BaseException:
+            valid = attr_type != "Derived"
+            if valid:                 
+                try:
+                    if isinstance(value, unicode):
+                        value = value.encode("utf-8")
+                except BaseException:
+                    pass
+                    
+                try:
+                    if attr_type != "Derived":
+                        getattr(self.wrapped_data, "setArgumentAs%s" % attr_type)(idx, entity_instance.unwrap_value(value))
+                except BaseException as e:
+                    valid = False
+
+            if not valid:
                 raise ValueError("Expected %s for attribute %s.%s, got %r" % (
                     real_attr_type, self.is_a(), self.attribute_name(idx), value))
+
         return value
 
     def __len__(self):
diff --git a/src/ifcwrap/IfcParseWrapper.i b/src/ifcwrap/IfcParseWrapper.i
index 174921f81c..67616f0f54 100644
--- a/src/ifcwrap/IfcParseWrapper.i
+++ b/src/ifcwrap/IfcParseWrapper.i
@@ -62,6 +62,9 @@ static IfcUtil::ArgumentType helper_fn_attribute_type(const IfcUtil::IfcBaseClas
 	const IfcParse::parameter_type* pt = 0;
 	if (inst->declaration().as_entity()) {
 		pt = inst->declaration().as_entity()->attribute_by_index(i)->type_of_attribute();
+		if (inst->declaration().as_entity()->derived()[i]) {
+			return IfcUtil::Argument_DERIVED;
+		}
 	} else if (inst->declaration().as_type_declaration() && i == 0) {
 		pt = inst->declaration().as_type_declaration()->declared_type();
 	}