diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7dd755e6b31..126175fb2d2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,7 @@ Ansible Changes By Release
   - Also added an ansible-config CLI to allow for listing config options and dumping current config (including origin)
   - TODO: build upon this to add many features detailed in ansible-config proposal https://github.com/ansible/proposals/issues/35
 * Windows modules now support the use of multiple shared module_utils files in the form of Powershell modules (.psm1), via `#Requires -Module Ansible.ModuleUtils.Whatever.psm1`
+* Python module argument_spec now supports custom validation logic by accepting a callable as the `type` argument.
 
 ### Deprecations
 * The behaviour when specifying `--tags` (or `--skip-tags`) multiple times on the command line
diff --git a/lib/ansible/module_utils/basic.py b/lib/ansible/module_utils/basic.py
index 0f25c6c7783..456cb4589eb 100644
--- a/lib/ansible/module_utils/basic.py
+++ b/lib/ansible/module_utils/basic.py
@@ -1874,22 +1874,28 @@ class AnsibleModule(object):
             wanted = v.get('type', None)
             if k not in param:
                 continue
-            if wanted is None:
-                # Mostly we want to default to str.
-                # For values set to None explicitly, return None instead as
-                # that allows a user to unset a parameter
-                if param[k] is None:
-                    continue
-                wanted = 'str'
 
             value = param[k]
             if value is None:
                 continue
 
-            try:
-                type_checker = self._CHECK_ARGUMENT_TYPES_DISPATCHER[wanted]
-            except KeyError:
-                self.fail_json(msg="implementation error: unknown type %s requested for %s" % (wanted, k))
+            if not callable(wanted):
+                if wanted is None:
+                    # Mostly we want to default to str.
+                    # For values set to None explicitly, return None instead as
+                    # that allows a user to unset a parameter
+                    if param[k] is None:
+                        continue
+                    wanted = 'str'
+                try:
+                    type_checker = self._CHECK_ARGUMENT_TYPES_DISPATCHER[wanted]
+                except KeyError:
+                    self.fail_json(msg="implementation error: unknown type %s requested for %s" % (wanted, k))
+            else:
+                # set the type_checker to the callable, and reset wanted to the callable's name (or type if it doesn't have one, ala MagicMock)
+                type_checker = wanted
+                wanted = getattr(wanted, '__name__', to_native(type(wanted)))
+
             try:
                 param[k] = type_checker(value)
             except (TypeError, ValueError):
diff --git a/test/units/module_utils/basic/test_argument_spec.py b/test/units/module_utils/basic/test_argument_spec.py
new file mode 100644
index 00000000000..f6f9689f726
--- /dev/null
+++ b/test/units/module_utils/basic/test_argument_spec.py
@@ -0,0 +1,49 @@
+# Copyright (c) 2017 Ansible Project
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import (absolute_import, division)
+__metaclass__ = type
+
+import json
+
+from ansible.compat.tests import unittest
+from ansible.compat.tests.mock import MagicMock
+from units.mock.procenv import swap_stdin_and_argv, swap_stdout
+from ansible.module_utils import basic
+
+
+class TestCallableTypeValidation(unittest.TestCase):
+    def setUp(self):
+        args = json.dumps(dict(ANSIBLE_MODULE_ARGS=dict(arg="42")))
+        self.stdin_swap_ctx = swap_stdin_and_argv(stdin_data=args)
+        self.stdin_swap_ctx.__enter__()
+
+        # since we can't use context managers and "with" without overriding run(), call them directly
+        self.stdout_swap_ctx = swap_stdout()
+        self.fake_stream = self.stdout_swap_ctx.__enter__()
+
+        basic._ANSIBLE_ARGS = None
+
+    def tearDown(self):
+        # since we can't use context managers and "with" without overriding run(), call them directly to clean up
+        self.stdin_swap_ctx.__exit__(None, None, None)
+        self.stdout_swap_ctx.__exit__(None, None, None)
+
+    def test_validate_success(self):
+        mock_validator = MagicMock(return_value=42)
+        m = basic.AnsibleModule(argument_spec=dict(
+            arg=dict(type=mock_validator)
+        ))
+
+        self.assertTrue(mock_validator.called)
+        self.assertEqual(m.params['arg'], 42)
+        self.assertEqual(type(m.params['arg']), int)
+
+    def test_validate_fail(self):
+        mock_validator = MagicMock(side_effect=TypeError("bad conversion"))
+        with self.assertRaises(SystemExit) as ecm:
+            m = basic.AnsibleModule(argument_spec=dict(
+                arg=dict(type=mock_validator)
+            ))
+
+        self.assertIn("bad conversion", json.loads(self.fake_stream.getvalue())['msg'])