diff --git a/src/x_class_builder.cpp b/src/x_class_builder.cpp
new file mode 100644
index 00000000..cf81a3f7
--- /dev/null
+++ b/src/x_class_builder.cpp
@@ -0,0 +1,118 @@
+# include <boost/python/x_class_builder.hpp>
+namespace python = boost::python;
+# include <stdio.h> // MSVC6.0SP4 does not know std::fprintf
+# include <string.h> // MSVC6.0SP4 does not know std::strcmp
+
+namespace {
+
+  PyObject *get_module_dict(const char *module_name)
+  {
+    python::ref module_obj(PyImport_ImportModule((char*) module_name));
+    PyObject *module_dict = PyModule_GetDict(module_obj.get());
+    if (module_dict == 0) throw python::import_error();
+    return module_dict;
+  }
+}
+
+namespace boost { namespace python { namespace detail {
+
+#ifndef SPECIAL_PYCVTSOBJECT
+
+void *import_converters(const std::string& module_name,
+                        const std::string& klass_name,
+                        const std::string& attribute_name)
+{
+  static std::string err;
+  PyObject *module_dict
+    = get_module_dict(const_cast<char*>(module_name.c_str()));
+  PyObject *klass
+    = PyDict_GetItemString(module_dict, const_cast<char*>(klass_name.c_str()));
+  if (klass == 0) {
+    err = std::string("module ") + module_name + " has no attribute "
+          + klass_name;
+    PyErr_SetString(PyExc_RuntimeError, const_cast<char*>(err.c_str()));
+    throw python::import_error();
+  }
+  python::ref c_obj(PyObject_GetAttrString(klass,
+    const_cast<char*>(attribute_name.c_str())), ref::null_ok);
+  if (c_obj.get() == 0) {
+    err = std::string("object ") + module_name + "." + klass_name
+          + " has no attribute " + attribute_name;
+    PyErr_SetString(PyExc_RuntimeError, const_cast<char*>(err.c_str()));
+    throw python::import_error();
+  }
+  if (! PyCObject_Check(c_obj.get())) {
+    err = std::string("object ") + module_name + "." + klass_name + "."
+          + attribute_name + " is not a PyCObject";
+    PyErr_SetString(PyExc_RuntimeError, const_cast<char*>(err.c_str()));
+    throw python::import_error();
+  }
+  return PyCObject_AsVoidPtr(c_obj.get());
+}
+
+#else
+
+PyObject *new_import_converters(const std::string& module_name,
+                                const std::string& klass_name,
+                                const std::string& attribute_name)
+{
+  static std::string err;
+  PyObject *module_dict
+    = get_module_dict(const_cast<char*>(module_name.c_str()));
+  PyObject *klass
+    = PyDict_GetItemString(module_dict, const_cast<char*>(klass_name.c_str()));
+  if (klass == 0) {
+    err = std::string("module ") + module_name + " has no attribute "
+          + klass_name;
+    PyErr_SetString(PyExc_RuntimeError, const_cast<char*>(err.c_str()));
+    throw python::import_error();
+  }
+  python::ref cvts_obj(PyObject_GetAttrString(klass,
+    const_cast<char*>(attribute_name.c_str())), ref::null_ok);
+  if (cvts_obj.get() == 0) {
+    err = std::string("object ") + module_name + "." + klass_name
+          + " has no attribute " + attribute_name;
+    PyErr_SetString(PyExc_RuntimeError, const_cast<char*>(err.c_str()));
+    throw python::import_error();
+  }
+  // Weak point: direct access to ob_type->tp_name
+  if (strcmp(cvts_obj->ob_type->tp_name, "PyCvtsObject") != 0) {
+    err = std::string("object ") + module_name + "." + klass_name + "."
+          + attribute_name + " is not a PyCvtsObject";
+    PyErr_SetString(PyExc_RuntimeError, const_cast<char*>(err.c_str()));
+    throw python::import_error();
+  }
+  return cvts_obj.release();
+}
+
+#endif // SPECIAL_PYCVTSOBJECT
+
+void check_export_converters_api(const int importing_major,
+                                 const int importing_minor,
+                                 const int imported_major,
+                                 const int imported_minor)
+{
+  if (importing_major != imported_major) {
+    // Python uses fprintf(stderr, ...) for API warnings.
+    fprintf(stderr,
+      "Fatal: EXPORT_CONVERTERS_API mismatch:"
+      " Importing module = %d.%d"
+      " Imported module = %d.%d\n",
+      importing_major, importing_minor,
+      imported_major, imported_minor);
+    PyErr_SetString(PyExc_RuntimeError,
+      "Fatal: EXPORT_CONVERTERS_API mismatch");
+    throw import_error();
+  }
+  if (importing_minor != imported_minor) {
+    // Python uses fprintf(stderr, ...) for API warnings.
+    fprintf(stderr,
+      "Warning: EXPORT_CONVERTERS_API mismatch:"
+      " Importing module = %d.%d"
+      " Imported module = %d.%d\n",
+      importing_major, importing_minor,
+      imported_major, imported_minor);
+  }
+}
+
+}}} // namespace boost::python::detail