diff --git a/pydu/dict.py b/pydu/dict.py
index 26d3569..ef2522e 100644
--- a/pydu/dict.py
+++ b/pydu/dict.py
@@ -67,7 +67,7 @@ class CaseInsensitiveDict(collections.MutableMapping):
     behavior is undefined.
     """
     def __init__(self, data=None, **kwargs):
-        self._store = dict()
+        self._store = {}
         if data is None:
             data = {}
         self.update(data, **kwargs)
diff --git a/pydu/dict.pyi b/pydu/dict.pyi
new file mode 100644
index 0000000..ef07569
--- /dev/null
+++ b/pydu/dict.pyi
@@ -0,0 +1,8 @@
+import collections
+from typing import Iterable, Tuple, Any, Optional
+
+
+class CaseInsensitiveDict(collections.MutableMapping):
+    _store = ... # type: dict
+    def __init__(self, data: Optional(dict), **kwargs) -> None: ...
+    def lower_items(self) -> Iterable[Tuple[str, Any]]: ...