diff --git a/CHANGES b/CHANGES
index e6888146c..32ce16917 100644
--- a/CHANGES
+++ b/CHANGES
@@ -19,6 +19,7 @@ Features added
 Bugs fixed
 ----------
 
+* #7886: autodoc: TypeError is raised on mocking generic-typed classes
 * #7839: autosummary: cannot handle umlauts in function names
 * #7865: autosummary: Failed to extract summary line when abbreviations found
 * #7866: autosummary: Failed to extract correct summary line when docstring
diff --git a/sphinx/ext/autodoc/mock.py b/sphinx/ext/autodoc/mock.py
index 98a3a3a96..40258a135 100644
--- a/sphinx/ext/autodoc/mock.py
+++ b/sphinx/ext/autodoc/mock.py
@@ -52,8 +52,8 @@ class _MockObject:
     def __mro_entries__(self, bases: Tuple) -> Tuple:
         return (self.__class__,)
 
-    def __getitem__(self, key: str) -> "_MockObject":
-        return _make_subclass(key, self.__display_name__, self.__class__)()
+    def __getitem__(self, key: Any) -> "_MockObject":
+        return _make_subclass(str(key), self.__display_name__, self.__class__)()
 
     def __getattr__(self, key: str) -> "_MockObject":
         return _make_subclass(key, self.__display_name__, self.__class__)()
diff --git a/tests/test_ext_autodoc_mock.py b/tests/test_ext_autodoc_mock.py
index 4760493cf..a29170f75 100644
--- a/tests/test_ext_autodoc_mock.py
+++ b/tests/test_ext_autodoc_mock.py
@@ -11,6 +11,7 @@
 import abc
 import sys
 from importlib import import_module
+from typing import TypeVar
 
 import pytest
 
@@ -39,6 +40,7 @@ def test_MockObject():
     assert isinstance(mock.attr1.attr2, _MockObject)
     assert isinstance(mock.attr1.attr2.meth(), _MockObject)
 
+    # subclassing
     class SubClass(mock.SomeClass):
         """docstring of SubClass"""
 
@@ -51,6 +53,16 @@ def test_MockObject():
     assert obj.method() == "string"
     assert isinstance(obj.other_method(), SubClass)
 
+    # parametrized type
+    T = TypeVar('T')
+
+    class SubClass2(mock.SomeClass[T]):
+        """docstring of SubClass"""
+
+    obj2 = SubClass2()
+    assert SubClass2.__doc__ == "docstring of SubClass"
+    assert isinstance(obj2, SubClass2)
+
 
 def test_mock():
     modname = 'sphinx.unknown'