diff --git a/Lib/inspect.py b/Lib/inspect.py
index d6bd8cd..b1a2cd2 100644
--- a/Lib/inspect.py
+++ b/Lib/inspect.py
@@ -1528,6 +1528,12 @@ def signature(obj):
                 init = _get_user_defined_method(obj, '__init__')
                 if init is not None:
                     sig = signature(init)
+
+        if sig is None and obj is not object and type not in obj.__mro__:
+            # We have a class (not metaclass), but no user-defined
+            # __init__ or __new__ for it
+            return Signature()
+
     elif not isinstance(obj, _NonUserDefinedCallables):
         # An object with __call__
         # We also check that the 'obj' is not an instance of
diff --git a/Lib/test/test_inspect.py b/Lib/test/test_inspect.py
index 1bfe724..798bf46 100644
--- a/Lib/test/test_inspect.py
+++ b/Lib/test/test_inspect.py
@@ -1964,6 +1964,12 @@ class TestSignatureObject(unittest.TestCase):
                            ('bar', 2, ..., "keyword_only")),
                           ...))
 
+        # Test classes without user-defined __init__ or __new__
+        class C: pass
+        self.assertEqual(self.signature(C), ((), ...))
+        class D(C): pass
+        self.assertEqual(self.signature(D), self.signature(C))
+
     def test_signature_on_callable_objects(self):
         class Foo:
             def __call__(self, a):