diff --git a/src/core/core.cpp b/src/core/core.cpp
index 4f9d672..cd3ed7e 100644
--- a/src/core/core.cpp
+++ b/src/core/core.cpp
@@ -11,8 +11,8 @@ void define_core(py::module& m) {
 
 void define_parse(py::module& m) {
     // Parse formulas
-    m.def("parse_properties", &storm::parsePropertiesForExplicit, "Parse explicit formulas", py::arg("formula_string"), py::arg("property_filter") = nullptr);
-    m.def("parse_properties_for_prism_program", &storm::parsePropertiesForPrismProgram, "Parse formulas for prism program", py::arg("formula_string"), py::arg("prism_program"), py::arg("property_filter") = nullptr);
+    m.def("parse_properties", &storm::parsePropertiesForExplicit, "Parse explicit formulas", py::arg("formula_string"), py::arg("property_filter") = boost::none);
+    m.def("parse_properties_for_prism_program", &storm::parsePropertiesForPrismProgram, "Parse formulas for prism program", py::arg("formula_string"), py::arg("prism_program"), py::arg("property_filter") = boost::none);
 
     // Pair <Model,Formulas>
     py::class_<storm::storage::ModelFormulasPair>(m, "ModelFormulasPair", "Pair of model and formulas")
diff --git a/src/mod_core.cpp b/src/mod_core.cpp
index 8f96262..122439b 100644
--- a/src/mod_core.cpp
+++ b/src/mod_core.cpp
@@ -16,6 +16,7 @@ PYBIND11_PLUGIN(core) {
     
     
     define_core(m);
+    define_property(m);
     define_parse(m);
     define_build(m);
     define_result(m);