diff -r 838c4df236cd -r 02a99370f6b3 pypy/module/__builtin__/compiling.py
--- a/pypy/module/__builtin__/compiling.py      Tue Sep 17 17:03:35 2019 +0300
+++ b/pypy/module/__builtin__/compiling.py      Tue Sep 24 17:27:53 2019 +0200
@@ -96,13 +96,33 @@
     frame = space.getexecutioncontext().gettopframe()
     frame.exec_(w_prog, w_globals, w_locals)

+def _update_bases(space, w_bases):
+    bases_w = space.listview(w_bases)
+    new_bases_w = []
+    changed = False
+    for w_base in bases_w:
+        w_meth = space.lookup(w_base, '__mro_entries__')
+        if w_meth is not None:
+            new_base_w = space.get_and_call_function(w_meth, w_base, w_bases)
+            if not space.isinstance_w(new_base_w, space.w_tuple):
+                raise oefmt(space.w_TypeError, "__mro_entries__ must return a tuple")
+            new_bases_w.extend(space.fixedview(new_base_w))
+            changed = True
+        else:
+            new_bases_w.append(w_base)
+    if not changed:
+        return bases_w
+    return new_bases_w
+
 def build_class(space, w_func, w_name, __args__):
     from pypy.objspace.std.typeobject import _calculate_metaclass, W_TypeObject
     from pypy.interpreter.nestedscope import Cell
     if not isinstance(w_func, Function):
         raise oefmt(space.w_TypeError, "__build_class__: func must be a function")
-    bases_w, kwds_w = __args__.unpack()
-    w_bases = space.newtuple(bases_w)
+    orig_bases_w, kwds_w = __args__.unpack()
+    w_orig_bases = space.newtuple(orig_bases_w)
+    bases_w = _update_bases(space, w_orig_bases)
+    w_bases = space.newtuple(bases_w[:])
     w_meta = kwds_w.pop('metaclass', None)
     if w_meta is not None:
         isclass = space.isinstance_w(w_meta, space.w_type)
@@ -144,6 +164,8 @@
     frame = space.createframe(code, w_func.w_func_globals, w_func)
     frame.setdictscope(w_namespace)
     w_cell = frame.run()
+    if bases_w is not orig_bases_w:
+        space.setitem(w_namespace, space.newtext("__orig_bases__"), w_orig_bases)
     keywords = kwds_w.keys()
     args = Arguments(space,
                      args_w=[w_name, w_bases, w_namespace],


diff -r 838c4df236cd -r 02a99370f6b3 pypy/objspace/std/typeobject.py
--- a/pypy/objspace/std/typeobject.py   Tue Sep 17 17:03:35 2019 +0300
+++ b/pypy/objspace/std/typeobject.py   Tue Sep 24 17:27:53 2019 +0200
@@ -808,6 +808,11 @@
     # above to be seen by the jit.
     _check_new_args(space, w_name, w_bases, w_dict)
     bases_w = space.fixedview(w_bases)
+    for w_base in bases_w:
+        if space.lookup(w_base, '__mro_entries__') is not None:
+            raise oefmt(space.w_TypeError,
+                        "type() doesn't support MRO entry resolution; "
+                        "use types.new_class()")

     w_winner = _calculate_metaclass(space, w_typetype, bases_w)
     if not space.is_w(w_winner, w_typetype):