diff --git a/abc.py b/abc.py
index ba6bcd5e19373c6156a5c0685c730cc9db307e97..2c32876e1af2da3c36207b7fc8177b3d62b7abd7 100644
--- a/abc.py
+++ b/abc.py
@@ -29,7 +29,7 @@ class ParametersABC(ABC):
         for k, v in kwargs.items():
             setattr(self, k, v)
 
-    def to_dict(self, iterable="null"):
+    def to_dict(self, iterable="null") -> t.Dict:
         """
         Recursive function to return a nested dictionary of the
         attributes of the class instance.