diff --git a/Include/abstract.h b/Include/abstract.h
index 04c007a..f3bc8bc 100644
--- a/Include/abstract.h
+++ b/Include/abstract.h
@@ -1377,6 +1377,11 @@
       /* issubclass(object, typeorclass) */
 
 
+PyAPI_FUNC(int) _PyObject_RealIsInstance(PyObject *inst, PyObject *cls);
+
+PyAPI_FUNC(int) _PyObject_RealIsSubclass(PyObject *derived, PyObject *cls);
+
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index 8fed220..3e0955f 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -88,15 +88,21 @@
             pass
         b = B()
         self.assertEqual(issubclass(B, A), False)
+        self.assertEqual(issubclass(B, (A,)), False)
         self.assertEqual(isinstance(b, A), False)
+        self.assertEqual(isinstance(b, (A,)), False)
         A.register(B)
         self.assertEqual(issubclass(B, A), True)
+        self.assertEqual(issubclass(B, (A,)), True)
         self.assertEqual(isinstance(b, A), True)
+        self.assertEqual(isinstance(b, (A,)), True)
         class C(B):
             pass
         c = C()
         self.assertEqual(issubclass(C, A), True)
+        self.assertEqual(issubclass(C, (A,)), True)
         self.assertEqual(isinstance(c, A), True)
+        self.assertEqual(isinstance(c, (A,)), True)
 
     def test_isinstance_invalidation(self):
         class A:
@@ -105,20 +111,26 @@
             pass
         b = B()
         self.assertEqual(isinstance(b, A), False)
+        self.assertEqual(isinstance(b, (A,)), False)
         A.register(B)
         self.assertEqual(isinstance(b, A), True)
+        self.assertEqual(isinstance(b, (A,)), True)
 
     def test_registration_builtins(self):
         class A:
             __metaclass__ = abc.ABCMeta
         A.register(int)
         self.assertEqual(isinstance(42, A), True)
+        self.assertEqual(isinstance(42, (A,)), True)
         self.assertEqual(issubclass(int, A), True)
+        self.assertEqual(issubclass(int, (A,)), True)
         class B(A):
             pass
         B.register(basestring)
         self.assertEqual(isinstance("", A), True)
+        self.assertEqual(isinstance("", (A,)), True)
         self.assertEqual(issubclass(str, A), True)
+        self.assertEqual(issubclass(str, (A,)), True)
 
     def test_registration_edge_cases(self):
         class A:
@@ -141,29 +153,40 @@
         class A:
             __metaclass__ = abc.ABCMeta
         self.failUnless(issubclass(A, A))
+        self.failUnless(issubclass(A, (A,)))
         class B:
             __metaclass__ = abc.ABCMeta
         self.failIf(issubclass(A, B))
+        self.failIf(issubclass(A, (B,)))
         self.failIf(issubclass(B, A))
+        self.failIf(issubclass(B, (A,)))
         class C:
             __metaclass__ = abc.ABCMeta
         A.register(B)
         class B1(B):
             pass
         self.failUnless(issubclass(B1, A))
+        self.failUnless(issubclass(B1, (A,)))
         class C1(C):
             pass
         B1.register(C1)
         self.failIf(issubclass(C, B))
+        self.failIf(issubclass(C, (B,)))
         self.failIf(issubclass(C, B1))
+        self.failIf(issubclass(C, (B1,)))
         self.failUnless(issubclass(C1, A))
+        self.failUnless(issubclass(C1, (A,)))
         self.failUnless(issubclass(C1, B))
+        self.failUnless(issubclass(C1, (B,)))
         self.failUnless(issubclass(C1, B1))
+        self.failUnless(issubclass(C1, (B1,)))
         C1.register(int)
         class MyInt(int):
             pass
         self.failUnless(issubclass(MyInt, A))
+        self.failUnless(issubclass(MyInt, (A,)))
         self.failUnless(isinstance(42, A))
+        self.failUnless(isinstance(42, (A,)))
 
     def test_all_new_methods_are_called(self):
         class A:
diff --git a/Lib/test/test_exceptions.py b/Lib/test/test_exceptions.py
index c3a9308..0576b62 100644
--- a/Lib/test/test_exceptions.py
+++ b/Lib/test/test_exceptions.py
@@ -333,7 +333,19 @@
                 return g()
             except ValueError:
                 return -1
-        self.assertRaises(RuntimeError, g)
+
+        # The test prints an unraisable recursion error when
+        # doing "except ValueError", this is because subclass
+        # checking has recursion checking too.
+        with captured_output("stderr"):
+            try:
+                g()
+            except RuntimeError:
+                pass
+            except:
+                self.fail("Should have raised KeyError")
+            else:
+                self.fail("Should have raised KeyError")
 
     def testUnicodeStrUsage(self):
         # Make sure both instances and classes have a str and unicode
@@ -363,12 +375,20 @@
             except KeyError:
                 pass
             except:
-                self.fail("Should have raised TypeError")
+                self.fail("Should have raised KeyError")
             else:
-                self.fail("Should have raised TypeError")
-        self.assertEqual(stderr.getvalue(),
-                         "Exception ValueError: ValueError() in "
-                         "<type 'exceptions.KeyError'> ignored\n")
+                self.fail("Should have raised KeyError")
+
+        with captured_output("stderr") as stderr:
+            def g():
+                try:
+                    return g()
+                except RuntimeError:
+                    return sys.exc_info()
+            e, v, tb = g()
+            self.assert_(e is RuntimeError, e)
+            self.assert_("maximum recursion depth exceeded" in str(v), v)
+
 
 def test_main():
     run_unittest(ExceptionTests)
diff --git a/Lib/test/test_typechecks.py b/Lib/test/test_typechecks.py
index 21be62d..32aa660 100644
--- a/Lib/test/test_typechecks.py
+++ b/Lib/test/test_typechecks.py
@@ -41,26 +41,39 @@
 
     def testIsSubclassBuiltin(self):
         self.assertEqual(issubclass(int, Integer), True)
+        self.assertEqual(issubclass(int, (Integer,)), True)
         self.assertEqual(issubclass(float, Integer), False)
+        self.assertEqual(issubclass(float, (Integer,)), False)
 
     def testIsInstanceBuiltin(self):
         self.assertEqual(isinstance(42, Integer), True)
+        self.assertEqual(isinstance(42, (Integer,)), True)
         self.assertEqual(isinstance(3.14, Integer), False)
+        self.assertEqual(isinstance(3.14, (Integer,)), False)
 
     def testIsInstanceActual(self):
         self.assertEqual(isinstance(Integer(), Integer), True)
+        self.assertEqual(isinstance(Integer(), (Integer,)), True)
 
     def testIsSubclassActual(self):
         self.assertEqual(issubclass(Integer, Integer), True)
+        self.assertEqual(issubclass(Integer, (Integer,)), True)
 
     def testSubclassBehavior(self):
         self.assertEqual(issubclass(SubInt, Integer), True)
+        self.assertEqual(issubclass(SubInt, (Integer,)), True)
         self.assertEqual(issubclass(SubInt, SubInt), True)
+        self.assertEqual(issubclass(SubInt, (SubInt,)), True)
         self.assertEqual(issubclass(Integer, SubInt), False)
+        self.assertEqual(issubclass(Integer, (SubInt,)), False)
         self.assertEqual(issubclass(int, SubInt), False)
+        self.assertEqual(issubclass(int, (SubInt,)), False)
         self.assertEqual(isinstance(SubInt(), Integer), True)
+        self.assertEqual(isinstance(SubInt(), (Integer,)), True)
         self.assertEqual(isinstance(SubInt(), SubInt), True)
+        self.assertEqual(isinstance(SubInt(), (SubInt,)), True)
         self.assertEqual(isinstance(42, SubInt), False)
+        self.assertEqual(isinstance(42, (SubInt,)), False)
 
     def testInfiniteRecursionCaughtProperly(self):
         e = Evil()
diff --git a/Misc/NEWS b/Misc/NEWS
index f1aec99..822d1c9 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,13 @@
 Core and Builtins
 -----------------
 
+- Issue #2534: speed up isinstance() and issubclass() by 50-70%, so as to 
+  match Python 2.5 speed despite the __instancecheck__ / __subclasscheck__
+  mechanism. In the process, fix a bug where isinstance() and issubclass(),
+  when given a tuple of classes as second argument, were looking up
+  __instancecheck__ / __subclasscheck__ on the tuple rather than on each
+  type object.
+
 - Fix crashes on memory allocation failure found with failmalloc.
 
 - Fix memory leaks found with valgrind and update suppressions file.
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 68e1549..956c4f4 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2778,39 +2778,38 @@
 static int
 abstract_issubclass(PyObject *derived, PyObject *cls)
 {
-	PyObject *bases;
+	PyObject *bases = NULL;
 	Py_ssize_t i, n;
 	int r = 0;
 
-
-	if (derived == cls)
-		return 1;
-
-	if (PyTuple_Check(cls)) {
-		/* Not a general sequence -- that opens up the road to
-		   recursion and stack overflow. */
-		n = PyTuple_GET_SIZE(cls);
-		for (i = 0; i < n; i++) {
-			if (derived == PyTuple_GET_ITEM(cls, i))
-				return 1;
+	while (1) {
+		if (derived == cls)
+			return 1;
+		bases = abstract_get_bases(derived);
+		if (bases == NULL) {
+			if (PyErr_Occurred())
+				return -1;
+			return 0;
 		}
+		n = PyTuple_GET_SIZE(bases);
+		if (n == 0) {
+			Py_DECREF(bases);
+			return 0;
+		}
+		/* Avoid recursivity in the single inheritance case */
+		if (n == 1) {
+			derived = PyTuple_GET_ITEM(bases, 0);
+			Py_DECREF(bases);
+			continue;
+		}
+		for (i = 0; i < n; i++) {
+			r = abstract_issubclass(PyTuple_GET_ITEM(bases, i), cls);
+			if (r != 0)
+				break;
+		}
+		Py_DECREF(bases);
+		return r;
 	}
-	bases = abstract_get_bases(derived);
-	if (bases == NULL) {
-		if (PyErr_Occurred())
-			return -1;
-		return 0;
-	}
-	n = PyTuple_GET_SIZE(bases);
-	for (i = 0; i < n; i++) {
-		r = abstract_issubclass(PyTuple_GET_ITEM(bases, i), cls);
-		if (r != 0)
-			break;
-	}
-
-	Py_DECREF(bases);
-
-	return r;
 }
 
 static int
@@ -2828,7 +2827,7 @@
 }
 
 static int
-recursive_isinstance(PyObject *inst, PyObject *cls, int recursion_depth)
+recursive_isinstance(PyObject *inst, PyObject *cls)
 {
 	PyObject *icls;
 	static PyObject *__class__ = NULL;
@@ -2862,25 +2861,6 @@
 			}
 		}
 	}
-	else if (PyTuple_Check(cls)) {
-		Py_ssize_t i, n;
-
-                if (!recursion_depth) {
-                    PyErr_SetString(PyExc_RuntimeError,
-                                    "nest level of tuple too deep");
-                    return -1;
-                }
-
-		n = PyTuple_GET_SIZE(cls);
-		for (i = 0; i < n; i++) {
-			retval = recursive_isinstance(
-                                    inst,
-                                    PyTuple_GET_ITEM(cls, i),
-                                    recursion_depth-1);
-			if (retval != 0)
-				break;
-		}
-	}
 	else {
 		if (!check_class(cls,
 			"isinstance() arg 2 must be a class, type,"
@@ -2910,6 +2890,24 @@
 	if (Py_TYPE(inst) == (PyTypeObject *)cls)
 		return 1;
 
+	if (PyTuple_Check(cls)) {
+		Py_ssize_t i;
+		Py_ssize_t n;
+		int r = 0;
+
+		if (Py_EnterRecursiveCall(" in __instancecheck__"))
+			return -1;
+		n = PyTuple_GET_SIZE(cls);
+		for (i = 0; i < n; ++i) {
+			PyObject *item = PyTuple_GET_ITEM(cls, i);
+			r = PyObject_IsInstance(inst, item);
+			if (r != 0)
+				/* either found it, or got an error */
+				break;
+		}
+		Py_LeaveRecursiveCall();
+		return r;
+	}
 	if (name == NULL) {
 		name = PyString_InternFromString("__instancecheck__");
 		if (name == NULL)
@@ -2934,47 +2932,28 @@
 		}
 		return ok;
 	}
-	return recursive_isinstance(inst, cls, Py_GetRecursionLimit());
+	return recursive_isinstance(inst, cls);
 }
 
 static  int
-recursive_issubclass(PyObject *derived, PyObject *cls, int recursion_depth)
+recursive_issubclass(PyObject *derived, PyObject *cls)
 {
 	int retval;
 
+ 	if (PyType_Check(cls) && PyType_Check(derived)) {
+ 		/* Fast path (non-recursive) */
+ 		return PyType_IsSubtype(
+			(PyTypeObject *)derived, (PyTypeObject *)cls);
+ 	}
 	if (!PyClass_Check(derived) || !PyClass_Check(cls)) {
 		if (!check_class(derived,
 				 "issubclass() arg 1 must be a class"))
 			return -1;
 
-		if (PyTuple_Check(cls)) {
-			Py_ssize_t i;
-			Py_ssize_t n = PyTuple_GET_SIZE(cls);
-
-                        if (!recursion_depth) {
-                            PyErr_SetString(PyExc_RuntimeError,
-                                            "nest level of tuple too deep");
-                            return -1;
-                        }
-			for (i = 0; i < n; ++i) {
-				retval = recursive_issubclass(
-                                            derived,
-                                            PyTuple_GET_ITEM(cls, i),
-                                            recursion_depth-1);
-				if (retval != 0) {
-					/* either found it, or got an error */
-					return retval;
-				}
-			}
-			return 0;
-		}
-		else {
-			if (!check_class(cls,
-					"issubclass() arg 2 must be a class"
-					" or tuple of classes"))
-				return -1;
-		}
-
+		if (!check_class(cls,
+				"issubclass() arg 2 must be a class"
+				" or tuple of classes"))
+			return -1;
 		retval = abstract_issubclass(derived, cls);
 	}
 	else {
@@ -2992,20 +2971,40 @@
 	static PyObject *name = NULL;
 	PyObject *t, *v, *tb;
 	PyObject *checker;
-	PyErr_Fetch(&t, &v, &tb);
 	
+ 	if (PyTuple_Check(cls)) {
+ 		Py_ssize_t i;
+ 		Py_ssize_t n;
+ 		int r = 0;
+ 
+ 		if (Py_EnterRecursiveCall(" in __subclasscheck__"))
+ 			return -1;
+ 		n = PyTuple_GET_SIZE(cls);
+ 		for (i = 0; i < n; ++i) {
+ 			PyObject *item = PyTuple_GET_ITEM(cls, i);
+ 			r = PyObject_IsSubclass(derived, item);
+ 			if (r != 0)
+ 				/* either found it, or got an error */
+ 				break;
+ 		}
+ 		Py_LeaveRecursiveCall();
+ 		return r;
+ 	}
 	if (name == NULL) {
 		name = PyString_InternFromString("__subclasscheck__");
 		if (name == NULL)
 			return -1;
 	}
+	PyErr_Fetch(&t, &v, &tb);
 	checker = PyObject_GetAttr(cls, name);
 	PyErr_Restore(t, v, tb);
 	if (checker != NULL) {
 		PyObject *res;
 		int ok = -1;
-		if (Py_EnterRecursiveCall(" in __subclasscheck__"))
+		if (Py_EnterRecursiveCall(" in __subclasscheck__")) {
+			Py_DECREF(checker);
 			return ok;
+		}
 		res = PyObject_CallFunctionObjArgs(checker, derived, NULL);
 		Py_LeaveRecursiveCall();
 		Py_DECREF(checker);
@@ -3015,7 +3014,19 @@
 		}
 		return ok;
 	}
-	return recursive_issubclass(derived, cls, Py_GetRecursionLimit());
+	return recursive_issubclass(derived, cls);
+}
+
+int
+_PyObject_RealIsInstance(PyObject *inst, PyObject *cls)
+{
+	return recursive_isinstance(inst, cls);
+}
+
+int
+_PyObject_RealIsSubclass(PyObject *derived, PyObject *cls)
+{
+	return recursive_issubclass(derived, cls);
 }
 
 
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index 02b5012..405b773 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -571,6 +571,49 @@
 	return result;
 }
 
+static PyObject *
+type___instancecheck__(PyObject *type, PyObject *inst)
+{
+	switch (_PyObject_RealIsInstance(inst, type)) {
+	case -1:
+		return NULL;
+	case 0:
+		Py_RETURN_FALSE;
+	default:
+		Py_RETURN_TRUE;
+	}
+}
+
+
+static PyObject *
+type_get_instancecheck(PyObject *type, void *context)
+{
+	static PyMethodDef ml = {"__instancecheck__",
+				 type___instancecheck__, METH_O };
+	return PyCFunction_New(&ml, type);
+}
+
+static PyObject *
+type___subclasscheck__(PyObject *type, PyObject *inst)
+{
+	switch (_PyObject_RealIsSubclass(inst, type)) {
+	case -1:
+		return NULL;
+	case 0:
+		Py_RETURN_FALSE;
+	default:
+		Py_RETURN_TRUE;
+	}
+}
+
+static PyObject *
+type_get_subclasscheck(PyObject *type, void *context)
+{
+	static PyMethodDef ml = {"__subclasscheck__",
+				 type___subclasscheck__, METH_O };
+	return PyCFunction_New(&ml, type);
+}
+
 static PyGetSetDef type_getsets[] = {
 	{"__name__", (getter)type_name, (setter)type_set_name, NULL},
 	{"__bases__", (getter)type_get_bases, (setter)type_set_bases, NULL},
@@ -579,6 +622,8 @@
 	 (setter)type_set_abstractmethods, NULL},
 	{"__dict__",  (getter)type_dict,  NULL, NULL},
 	{"__doc__", (getter)type_get_doc, NULL, NULL},
+	{"__instancecheck__", (getter)type_get_instancecheck, NULL, NULL},
+	{"__subclasscheck__", (getter)type_get_subclasscheck, NULL, NULL},
 	{0}
 };
 
diff --git a/Python/errors.c b/Python/errors.c
index 5d9cab5..c88a190 100644
--- a/Python/errors.c
+++ b/Python/errors.c
@@ -113,7 +113,6 @@
 		/* This function must not fail, so print the error here */
 		if (res == -1) {
 			PyErr_WriteUnraisable(err);
-			/* issubclass did not succeed */
 			res = 0;
 		}
 		PyErr_Restore(exception, value, tb);