diff --git a/pythonfmu/builder.py b/pythonfmu/builder.py
index a96d51b..da9275d 100644
--- a/pythonfmu/builder.py
+++ b/pythonfmu/builder.py
@@ -3,11 +3,11 @@
 import importlib
 import itertools
 import logging
-import re
 import shutil
 import sys
 import tempfile
 import zipfile
+import inspect
 from pathlib import Path
 from typing import Iterable, Optional, Tuple, Union
 from xml.dom.minidom import parseString
@@ -21,11 +21,21 @@
 logger = logging.getLogger(__name__)
 
 
-def get_class_name(file_name: Path) -> str:
-    with open(str(file_name), 'r') as file:
-        data = file.read()
-        return re.search(r'class (\w+)\(\s*Fmi2Slave\s*\)\s*:', data).group(1)
+def get_class_name(interface) -> str:
+    """Returns the name of the class derived from Fmi2Slave in the given interface module.
+    
+    Args:
+        interface: The module containing the classes to be inspected.
+    Returns:
+        str: The name of the class derived from Fmi2Slave, or None if no such class is found.
+    """
+    candidate, mro = None, []
+    for cl in [x for x in dir(interface) if inspect.isclass(getattr(interface, x))]: # get all classes in module and go through them
+        if any(m.__name__ == 'Fmi2Slave' for m in inspect.getmro(getattr(interface, cl))): # inspect the class hierarchy and return if 'Fmi2Slave' found
+            if getattr(interface, cl) not in mro: # must be a sub-class of the already registered (or first)
+                candidate, mro = cl, inspect.getmro(getattr(interface, cl))
 
+    return candidate
 
 def get_model_description(filepath: Path, module_name: str) -> Tuple[str, Element]:
     """Extract the FMU model description as XML.
@@ -45,7 +55,7 @@ def get_model_description(filepath: Path, module_name: str) -> Tuple[str, Elemen
         fmu_interface = importlib.util.module_from_spec(spec)
         spec.loader.exec_module(fmu_interface)
         # Instantiate the interface
-        class_name = get_class_name(filepath)
+        class_name = get_class_name(fmu_interface)
         instance = getattr(fmu_interface, class_name)(instance_name="dummyInstance", resources=str(filepath.parent))
     finally:
         sys.path.remove(str(filepath.parent))  # remove inserted temporary path
diff --git a/pythonfmu/pythonfmu-export/src/pythonfmu/PySlaveInstance.cpp b/pythonfmu/pythonfmu-export/src/pythonfmu/PySlaveInstance.cpp
index 4112808..c0bd190 100644
--- a/pythonfmu/pythonfmu-export/src/pythonfmu/PySlaveInstance.cpp
+++ b/pythonfmu/pythonfmu-export/src/pythonfmu/PySlaveInstance.cpp
@@ -1,4 +1,3 @@
-
 #include "pythonfmu/IPyState.hpp"
 #include "pythonfmu/PySlaveInstance.hpp"
 
@@ -8,6 +7,8 @@
 
 #include <fstream>
 #include <functional>
+#include <filesystem>
+#include <string>
 #include <mutex>
 #include <regex>
 #include <sstream>
@@ -24,19 +25,96 @@ inline std::string getline(const std::string& fileName)
     return line;
 }
 
-inline std::string findClassName(const std::string& fileName)
-{
+PyObject* findClass(const std::string& resources, const std::string& moduleName) {
+    // Initialize the Python interpreter
+    std::string filename = resources + "/" + moduleName + ".py";
+    std::string deepestFile = "";
+    int deepestChain = 0;
+
+    // Read and execute the Python file
+    std::ifstream file;
+    file.open(filename);
+            
+    if (!file.is_open()) {
+        return nullptr;
+    }
+
+    std::stringstream fileContents;
     std::string line;
-    std::ifstream infile(fileName);
-    std::string regexStr(R"(^class (\w+)\(\s*Fmi2Slave\s*\)\s*:)");
-    while (getline(infile, line)) {
-        std::smatch m;
-        std::regex re(regexStr);
-        if (std::regex_search(line, m, re)) {
-            return m[1];
+
+    while (std::getline(file, line)) {
+        fileContents << line << "\n";
+    }
+
+    // Compile python code so classes are added to the namespace
+    PyObject* pyModule = PyImport_ImportModule(moduleName.c_str());
+        
+    if (pyModule == nullptr) {
+        return nullptr;
+    }
+    PyObject* pGlobals = PyModule_GetDict(pyModule);
+    PyObject* pLocals = PyDict_New();
+    PyObject* pCode = Py_CompileString(fileContents.str().c_str(), moduleName.c_str(), Py_file_input);
+
+    if (pCode != NULL) {
+        PyObject* pResult = PyEval_EvalCode(pCode, pGlobals, pLocals);
+        Py_XDECREF(pResult);
+    } else {
+        PyErr_Print(); // Handle compilation error
+        Py_Finalize();
+        Py_DECREF(pGlobals);
+        Py_DECREF(pyModule);
+        Py_DECREF(pLocals);
+        Py_DECREF(pCode);
+        file.close();
+        return nullptr;
+    }
+
+    fileContents.clear();
+    PyObject* key, * value;
+    Py_ssize_t pos = 0;
+
+    while (PyDict_Next(pLocals, &pos, &key, &value)) {
+        // Check if element in namespace is a class
+        if (!PyType_Check(value)) {
+            continue;
+        }
+
+        PyObject* pMroAttribute = PyObject_GetAttrString(value, "__mro__");
+
+        if (pMroAttribute != NULL && PySequence_Check(pMroAttribute)) {
+            std::regex pattern ("<class '[^']+\\.([^']+)'");
+            PyObject* pMROList = PySequence_List(pMroAttribute);
+
+            for (Py_ssize_t i = 0; i < PyList_Size(pMROList); ++i) {
+                PyObject* pItem = PyList_GetItem(pMROList, i);
+                std::smatch match;
+                const char* className = PyBytes_AsString(PyUnicode_AsUTF8String(PyObject_Repr(pItem)));
+                        
+                std::string str (className);
+                bool isMatch = std::regex_search(str, match, pattern);
+
+                // If regex match is successfull, and found Fmi2Slave at the deepest level then update state
+                if (isMatch && i > deepestChain && match[1] == "Fmi2Slave") {
+                    deepestFile = PyBytes_AsString(PyUnicode_AsUTF8String(key));
+                    deepestChain = i;
+                }
+            }
         }
+        Py_DECREF(pMroAttribute);
     }
-    return "";
+
+    PyObject* pyClassName = Py_BuildValue("s", deepestFile.c_str());
+    PyObject* pyClass = PyObject_GetAttr(pyModule, pyClassName);
+
+    // Clean up Python objects
+    Py_DECREF(pCode);
+    Py_DECREF(pLocals);
+    Py_DECREF(pyModule);
+    Py_DECREF(pGlobals);
+    file.close();
+    Py_DECREF(pyClassName);
+    return pyClass;
 }
 
 inline void py_safe_run(const std::function<void(PyGILState_STATE gilState)>& f)
@@ -65,33 +143,17 @@ PySlaveInstance::PySlaveInstance(std::string instanceName, std::string resources
             handle_py_exception("[ctor] PyObject_GetAttrString", gilState);
         }
         int success = PyList_Insert(sys_path, 0, PyUnicode_FromString(resources_.c_str()));
+
         Py_DECREF(sys_path);
         if (success != 0) {
             handle_py_exception("[ctor] PyList_Insert", gilState);
         }
 
         std::string moduleName = getline(resources_ + "/slavemodule.txt");
-        PyObject* pModule = PyImport_ImportModule(moduleName.c_str());
-        if (pModule == nullptr) {
-            handle_py_exception("[ctor] PyImport_ImportModule", gilState);
-        }
-
-        std::string className = findClassName(resources_ + "/" + moduleName + ".py");
-        if (className.empty()) {
-            cleanPyObject();
-            throw cppfmu::FatalError("Unable to find class extending Fmi2Slave!");
-        }
-
-        PyObject* pyClassName = Py_BuildValue("s", className.c_str());
-        if (pyClassName == nullptr) {
-            handle_py_exception("[ctor] Py_BuildValue", gilState);
-        }
 
-        pClass_ = PyObject_GetAttr(pModule, pyClassName);
-        Py_DECREF(pyClassName);
-        Py_DECREF(pModule);
+        pClass_ = findClass(resources_, moduleName);
         if (pClass_ == nullptr) {
-            handle_py_exception("[ctor] PyObject_GetAttr", gilState);
+            handle_py_exception("[ctor] findClass", gilState);
         }
 
         initialize(gilState);