diff --git a/docs/validate.rst b/docs/validate.rst
index 6de8d80..25a7705 100644
--- a/docs/validate.rst
+++ b/docs/validate.rst
@@ -155,18 +155,19 @@ a ``types`` argument on construction that specifies additional types, or which
 can be used to specify a different set of Python types to map to a given JSON
 type.
 
-``jsonschema`` tries to be as general as possible by default. For instance,
-JSON defines a ``number`` type, which can be validated with a schema such as
-``{"type" : "number"}``. By default, this will validate correctly for instances
-of Python :class:`number.Number`\s. This includes in particular :class:`int`\s
-and :class:`float`\s, along with `decimal.Decimal` objects, :class:`complex`
-numbers etc. See the numbers_ module documentation for more details.
+``jsonschema`` tries to strike a balance between performance in the common case
+and generality. For instance, JSON defines a ``number`` type, which can be
+validated with a schema such as ``{"type" : "number"}``. By default, this will
+accept instances of Python :class:`number.Number`. This includes in particular
+:class:`int`\s and :class:`float`\s, along with `decimal.Decimal` objects,
+:class:`complex` numbers etc. See the numbers_ module documentation for more
+details. For ``integer`` and ``object``, however, rather than checking for
+``number.Integral`` and ``collections.Mapping``, ``jsonschema`` simply checks
+for ``int`` and ``dict``, since the former can introduce significant slowdown.
 
-For most purposes, if you want to add additional types as being acceptible for
-a validator, you should do so by inheriting from the relevant ``abc`` or by
-registering the existing class with the ``abc``. If this isn't an option, or if
-you otherwise prefer not doing so, :class:`IValidator`\s have a ``types``
-argument that can be used to provide additional or new types.
+If you *do* want the generality, or just want to add a few specific additional
+types as being acceptible for a validator, :class:`IValidator`\s have a
+``types`` argument that can be used to provide additional or new types.
 
 .. code-block:: python
 
diff --git a/jsonschema.py b/jsonschema.py
index 6147518..299514a 100644
--- a/jsonschema.py
+++ b/jsonschema.py
@@ -30,6 +30,7 @@ if PY3:
     from urllib.parse import unquote
     from urllib.request import urlopen
     basestring = unicode = str
+    long = int
     iteritems = operator.methodcaller("items")
 else:
     from itertools import izip as zip
@@ -38,11 +39,6 @@ else:
     import urlparse
     iteritems = operator.methodcaller("iteritems")
 
-try:
-    from collections import abc
-except ImportError:
-    import collections as abc
-
 
 FLOAT_TOLERANCE = 10 ** -15
 validators = {}
@@ -91,8 +87,8 @@ class Draft3Validator(object):
     """
 
     DEFAULT_TYPES = {
-        "array" : list, "boolean" : bool, "integer" : numbers.Integral,
-        "null" : type(None), "number" : numbers.Number, "object" : abc.Mapping,
+        "array" : list, "boolean" : bool, "integer" : (int, long),
+        "null" : type(None), "number" : numbers.Number, "object" : dict,
         "string" : basestring,
     }
 
diff --git a/perftest b/perftest
index 45ddc1e..f5dc5c4 100755
--- a/perftest
+++ b/perftest
@@ -6,22 +6,21 @@ A *very* basic performance test.
 
 from __future__ import print_function
 import argparse
+import textwrap
 import timeit
 
-from jsonschema import Draft3Validator, validate
-
-
 parser = argparse.ArgumentParser()
 parser.add_argument("-n", "--number", type=int, default=100)
 arguments = parser.parse_args()
 
-instance = schema = Draft3Validator.META_SCHEMA
-
 results = timeit.timeit(
+    number=arguments.number,
     # Validate the Draft 3 meta-schema against itself without meta-validating
     stmt="validate(instance, schema)",
-    setup="from __main__ import instance, schema, validate",
-    number=arguments.number,
+    setup=textwrap.dedent("""
+    from jsonschema import Draft3Validator, validate
+    instance = schema = Draft3Validator.META_SCHEMA
+    """),
 )
 
 print(
diff --git a/tests.py b/tests.py
index 859c1cd..d554874 100644
--- a/tests.py
+++ b/tests.py
@@ -17,7 +17,7 @@ except ImportError:
     import mock
 
 from jsonschema import (
-    PY3, abc, SchemaError, UnknownType, ValidationError, ErrorTree,
+    PY3, SchemaError, UnknownType, ValidationError, ErrorTree,
     Draft3Validator, FormatChecker, RefResolver, validate
 )
 
@@ -76,13 +76,6 @@ class TypesMixin(object):
     def test_string_a_bytestring_is_a_string(self):
         self.validator_class({"type" : "string"}).validate(b"foo")
 
-    def test_mappings_are_objects(self):
-        class Mapping(abc.Mapping):
-            def __getitem__(self): return 12
-            def __iter__(self): return iter([])
-            def __len__(self): return 12
-        self.validator_class({"type" : "object"}).validate(Mapping())
-
 
 class DecimalMixin(object):
     def test_it_can_validate_with_decimals(self):