diff --git a/pycstruct/pycstruct.py b/pycstruct/pycstruct.py
index b232661..c7ae5ac 100644
--- a/pycstruct/pycstruct.py
+++ b/pycstruct/pycstruct.py
@@ -504,7 +504,7 @@ def add(self, datatype, name, length=1, byteorder="", same_level=False, shape=No
            +------------+---------------+--------------------------------------+
 
         :param datatype: Element data type. See above.
-        :type datatype: str
+        :type datatype: str | _BaseDef
         :param name: Name of element. Needs to be unique.
         :type name: str
         :param length: Number of elements. If > 1 this is an array/list of