diff --git a/concrete/numpy/compilation/configuration.py b/concrete/numpy/compilation/configuration.py
index a5c168df0..074794b26 100644
--- a/concrete/numpy/compilation/configuration.py
+++ b/concrete/numpy/compilation/configuration.py
@@ -114,17 +114,20 @@ class Configuration:
                 raise TypeError(f"Unexpected keyword argument '{name}'")
 
             hint = hints[name]
+            expected = None
             is_correctly_typed = True
 
             if name == "insecure_key_cache_location":
                 if not (value is None or isinstance(value, str)):
                     is_correctly_typed = False
+                    expected = "Optional[str]"
 
             elif not isinstance(value, hint):  # type: ignore
                 is_correctly_typed = False
 
             if not is_correctly_typed:
-                expected = hint.__name__ if hasattr(hint, "__name__") else str(hint)
+                if expected is None:
+                    expected = hint.__name__ if hasattr(hint, "__name__") else str(hint)
                 raise TypeError(
                     f"Unexpected type for keyword argument '{name}' "
                     f"(expected '{expected}', got '{type(value).__name__}')"
diff --git a/tests/compilation/test_configuration.py b/tests/compilation/test_configuration.py
index 28b7ab329..6194c8dfc 100644
--- a/tests/compilation/test_configuration.py
+++ b/tests/compilation/test_configuration.py
@@ -72,7 +72,7 @@ def test_configuration_fork():
             {"insecure_key_cache_location": 3},
             TypeError,
             "Unexpected type for keyword argument 'insecure_key_cache_location' "
-            "(expected 'typing.Union[str, NoneType]', got 'int')",
+            "(expected 'Optional[str]', got 'int')",
         ),
     ],
 )