diff --git a/src/stringenum/_core.py b/src/stringenum/_core.py
index 91caa88..44e157b 100644
--- a/src/stringenum/_core.py
+++ b/src/stringenum/_core.py
@@ -18,7 +18,7 @@ class DuplicateFreeStrEnum(StrEnum):
     raising a `ValueError` if duplicates are found.
     """
 
-    def __init__(self, *args: object) -> None:
+    def __init__(self, *args: str) -> None:
         cls = self.__class__
 
         for member in cls:
diff --git a/tests/test_case_insensitive_strenum.py b/tests/test_case_insensitive_strenum.py
index dd4f857..f38b468 100644
--- a/tests/test_case_insensitive_strenum.py
+++ b/tests/test_case_insensitive_strenum.py
@@ -47,7 +47,7 @@ def test_invalid_enum_value() -> None:
         Color("invalid_color")
 
     with pytest.raises(ValueError):
-        Color(None)
+        Color(None) # type: ignore[arg-type]
 
 
 def test_invalid_enum_key() -> None:
diff --git a/tests/test_double_sided_case_insensitive_strenum.py b/tests/test_double_sided_case_insensitive_strenum.py
index d25b3da..5e91335 100644
--- a/tests/test_double_sided_case_insensitive_strenum.py
+++ b/tests/test_double_sided_case_insensitive_strenum.py
@@ -88,7 +88,7 @@ def test_value_error_on_invalid_lookup() -> None:
         Color("yellow")
 
     with pytest.raises(ValueError):
-        Color(None)
+        Color(None) # type: ignore[arg-type]
 
 
 def test_unique_on_each_side() -> None:
diff --git a/tests/test_double_sided_strenum.py b/tests/test_double_sided_strenum.py
index 56af42f..441c7be 100644
--- a/tests/test_double_sided_strenum.py
+++ b/tests/test_double_sided_strenum.py
@@ -66,7 +66,7 @@ def test_value_error_on_invalid_lookup() -> None:
         Color("Red_color")
 
     with pytest.raises(ValueError):
-        Color(None)
+        Color(None) # type: ignore[arg-type]
 
 
 def test_unique_on_each_side() -> None: