diff --git a/src/ifcparse/IfcUntypedEntity.cpp b/src/ifcparse/IfcUntypedEntity.cpp
index a7e62cbbf9..bd2ce55a67 100644
--- a/src/ifcparse/IfcUntypedEntity.cpp
+++ b/src/ifcparse/IfcUntypedEntity.cpp
@@ -61,6 +61,12 @@ void Ifc::IfcUntypedEntity::invalid_argument(unsigned int i, const std::string&
 	const std::string arg_name = Ifc2x3::Type::GetAttributeName(_type,i);
 	throw IfcException(t + " is not a valid type for '" + arg_name + "'");
 }
+void Ifc::IfcUntypedEntity::setArgument(unsigned int i) {
+	bool is_optional = Ifc2x3::Type::GetAttributeOptional(_type, i);
+	if (is_optional) {
+		writable_entity()->setArgument(i);
+	} else invalid_argument(i,"NONE");
+}
 void Ifc::IfcUntypedEntity::setArgument(unsigned int i, int v) {
 	IfcUtil::ArgumentType arg_type = Ifc2x3::Type::GetAttributeType(_type,i);
 	if (arg_type == Argument_INT) {
diff --git a/src/ifcparse/IfcUntypedEntity.h b/src/ifcparse/IfcUntypedEntity.h
index c1827a7c5e..0c6f663df8 100644
--- a/src/ifcparse/IfcUntypedEntity.h
+++ b/src/ifcparse/IfcUntypedEntity.h
@@ -27,6 +27,7 @@ namespace Ifc {
 		const char* getArgumentName(unsigned int i) const;
 		unsigned getArgumentIndex(const std::string& a) const;
 
+		void setArgument(unsigned int iz);
 		void setArgument(unsigned int i, int v);
 		void setArgument(unsigned int i, bool v);
 		void setArgument(unsigned int i, double v);
diff --git a/src/ifcwrap/IfcPython.i b/src/ifcwrap/IfcPython.i
index 02179b3210..f0e58dbf4d 100644
--- a/src/ifcwrap/IfcPython.i
+++ b/src/ifcwrap/IfcPython.i
@@ -37,7 +37,7 @@
 %rename("get_argument_type") getArgumentType;
 %rename("get_argument_name") getArgumentName;
 %rename("get_argument_index") getArgumentIndex;
-%rename("set_argument") setArgument;
+%rename("_set_argument") setArgument;
 %rename("__repr__") toString;
 %rename("Entity") IfcUntypedEntity;
 
@@ -144,11 +144,16 @@
 		$self->AddEntity(e);
 	}
 	void write(const std::string& fn) {
-		std::ofstream f(fn.c_str());
+		std::ofstream f(fn);
 		f << (*$self);
 	}
 }
 
+%extend Ifc::IfcUntypedEntity {
+	%pythoncode %{
+	set_argument = lambda self,x,y: self._set_argument(x) if y is None else self._set_argument(x,y)
+	%}
+}
 
 namespace std {
    %template(Ints) vector<int>;
diff --git a/src/ifcwrap/Interface.h b/src/ifcwrap/Interface.h
index 043fcaf968..9eff58f00a 100644
--- a/src/ifcwrap/Interface.h
+++ b/src/ifcwrap/Interface.h
@@ -28,6 +28,7 @@ namespace Ifc {
 		const char* getArgumentName(unsigned int i) const;
 		unsigned getArgumentIndex(const std::string& a) const;
 
+		void setArgument(unsigned int i);
 		void setArgument(unsigned int i, int v);
 		void setArgument(unsigned int i, bool v);
 		void setArgument(unsigned int i, double v);