diff --git a/pybindgen/cppclass.py b/pybindgen/cppclass.py
index 97c1b82..808dce7 100644
--- a/pybindgen/cppclass.py
+++ b/pybindgen/cppclass.py
@@ -1416,7 +1416,7 @@ class CppClassParameter(CppClassParameterBase):
         else:
             implicit_conversion_sources = self.cpp_class.get_all_implicit_conversions()
             if not implicit_conversion_sources:
-                if self.default_value:
+                if self.default_value is not None:
                     self.py_name = wrapper.declarations.declare_variable(
                         self.cpp_class.pystruct+'*', self.name, 'NULL')
                     wrapper.parse_params.add_parameter(
@@ -1514,7 +1514,7 @@ class CppClassRefParameter(CppClassParameterBase):
             else:
                 implicit_conversion_sources = self.cpp_class.get_all_implicit_conversions()
                 if not (implicit_conversion_sources and self.is_const):
-                    if self.default_value:
+                    if self.default_value is not None:
                         self.py_name = wrapper.declarations.declare_variable(
                             self.cpp_class.pystruct+'*', self.name, 'NULL')
                         wrapper.parse_params.add_parameter(
@@ -1530,7 +1530,7 @@ class CppClassRefParameter(CppClassParameterBase):
                         wrapper.call_params.append(
                             '*((%s *) %s)->obj' % (self.cpp_class.pystruct, self.py_name))
                 else:
-                    if self.default_value:
+                    if self.default_value is not None:
                         warnings.warn("with implicit conversions, default value "
                                       "in C++ class reference parameters is ignored.")
                     self.py_name = wrapper.declarations.declare_variable(