diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index e1dbfdacf56337..0bb6750655380d 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -700,7 +700,7 @@ def __getattr__(self, name):
             if name.startswith(('assert', 'assret', 'asert', 'aseert', 'assrt')) or name in _ATTRIB_DENY_LIST:
                 raise AttributeError(
                     f"{name!r} is not a valid assertion. Use a spec "
-                    f"for the mock if {name!r} is meant to be an attribute.")
+                    f"for the mock if {name!r} is meant to be an attribute")
 
         with NonCallableMock._lock:
             result = self._mock_children.get(name)
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-08-13-16-58-58.gh-issue-137716.ZcZSyi.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-08-13-16-58-58.gh-issue-137716.ZcZSyi.rst
new file mode 100644
index 00000000000000..82d8e1577905a7
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2025-08-13-16-58-58.gh-issue-137716.ZcZSyi.rst
@@ -0,0 +1 @@
+Fix double period in :exc:`AttributeError` message for invalid mock assertions