diff --git a/Doc/c-api/object.rst b/Doc/c-api/object.rst
index f71bfebdb2a19a..6c699ae61f931d 100644
--- a/Doc/c-api/object.rst
+++ b/Doc/c-api/object.rst
@@ -433,7 +433,9 @@ Object Protocol
 
    If *cls* has a :meth:`~type.__instancecheck__` method, it will be called to
    determine the subclass status as described in :pep:`3119`.  Otherwise, *inst*
-   is an instance of *cls* if its class is a subclass of *cls*.
+   is an instance of *cls* if its class is a subclass of *cls*. If *inst* is
+   an instance of *cls*, this will return ``1`` and will not call
+   :meth:`~type.__instancecheck__`.
 
    An instance *inst* can override what is considered its class by having a
    :attr:`~object.__class__` attribute.
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 27aedfa878af9a..a0f12ae5939bce 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -2965,7 +2965,11 @@ ABCs.
 
    Return true if *instance* should be considered a (direct or indirect)
    instance of *class*. If defined, called to implement ``isinstance(instance,
-   class)``.
+   cls)``.
+
+   .. note::
+      If ``type(instance) is cls`` then ``isinstance(instance, cls)`` is
+      always ``True`` and ``__instancecheck__`` is not called.
 
 
 .. method:: type.__subclasscheck__(self, subclass)