diff --git a/tinyml-modelmaker/tests/test_config_dict.py b/tinyml-modelmaker/tests/test_config_dict.py
index 1372f544..2255d786 100644
--- a/tinyml-modelmaker/tests/test_config_dict.py
+++ b/tinyml-modelmaker/tests/test_config_dict.py
@@ -44,3 +44,9 @@ def test_none_input(self):
         cfg = ConfigDict(None)
         # Should create an empty config without error
         assert isinstance(cfg, ConfigDict)
+
+    def test_constructor_args_deep_merge_nested_dict(self):
+        default = dict(training=dict(a=1, b=2))
+        user = dict(training=dict(b=99))
+        cfg = ConfigDict(default, user)
+        assert dict(cfg.training) == {"a": 1, "b": 99}
diff --git a/tinyml-modelmaker/tinyml_modelmaker/utils/config_dict.py b/tinyml-modelmaker/tinyml_modelmaker/utils/config_dict.py
index 953fa23d..d40e4cf2 100644
--- a/tinyml-modelmaker/tinyml_modelmaker/utils/config_dict.py
+++ b/tinyml-modelmaker/tinyml_modelmaker/utils/config_dict.py
@@ -57,7 +57,7 @@ def __init__(self, input=None, *args, **kwargs):
         # override the entries with args
         for value in args:
             if isinstance(value, (dict, ConfigDict)):
-                input_dict.update(value)
+                self._deep_merge(input_dict, value)
             #
         #
         # override the entries with kwargs
@@ -95,6 +95,17 @@ def __setstate__(self, state):
     def _initialize(self):
         pass
 
+    @staticmethod
+    def _deep_merge(target, source):
+        for key, value in source.items():
+            if key in target and isinstance(target[key], (dict, ConfigDict)) and isinstance(value, (dict, ConfigDict)):
+                ConfigDict._deep_merge(target[key], value)
+            else:
+                target[key] = value
+            #
+        #
+        return target
+
     def _parse_include_files(self, include_files, include_base_path):
         input_dict = {}
         include_files = list(include_files)