diff -r 03fc7449f204 Lib/inspect.py
--- a/Lib/inspect.py	Wed Jan 29 23:02:49 2014 -0800
+++ b/Lib/inspect.py	Thu Jan 30 11:47:00 2014 -0500
@@ -1601,6 +1601,23 @@
             obj in (type, object))
 
 
+def _signature_is_functionlike(obj):
+    # Internal helper to test if `obj` is a duck type of FunctionType
+
+    if not callable(obj):
+        return False
+
+    code = getattr(obj, '__code__', None)
+    defaults = getattr(obj, '__defaults__', None)
+    kwdefaults = getattr(obj, '__kwdefaults__', None)
+    annotations = getattr(obj, '__annotations__', None)
+
+    return (isinstance(code, types.CodeType) and
+            (defaults is None or isinstance(defaults, tuple)) and
+            (kwdefaults is None or isinstance(kwdefaults, dict)) and
+            isinstance(annotations, dict))
+
+
 def _signature_get_bound_param(spec):
     # Internal helper to get first parameter name from a
     # __text_signature__ of a builtin method, which should
@@ -1670,7 +1687,7 @@
     if _signature_is_builtin(obj):
         return Signature.from_builtin(obj)
 
-    if isinstance(obj, types.FunctionType):
+    if isfunction(obj) or _signature_is_functionlike(obj):
         return Signature.from_function(obj)
 
     if isinstance(obj, functools.partial):
@@ -2071,7 +2088,7 @@
     def from_function(cls, func):
         '''Constructs Signature for the given python function'''
 
-        if not isinstance(func, types.FunctionType):
+        if not (isfunction(func) or _signature_is_functionlike(func)):
             raise TypeError('{!r} is not a Python function'.format(func))
 
         Parameter = cls._parameter_cls
diff -r 03fc7449f204 Lib/test/test_inspect.py
--- a/Lib/test/test_inspect.py	Wed Jan 29 23:02:49 2014 -0800
+++ b/Lib/test/test_inspect.py	Thu Jan 30 11:47:00 2014 -0500
@@ -1736,6 +1736,33 @@
         with self.assertRaisesRegex(TypeError, 'is not a Python builtin'):
             inspect.Signature.from_builtin(42)
 
+    def test_signature_from_functionlike_object(self):
+        def func(a,b, *args, kwonly=True, kwonlyreq, **kwargs):
+            pass
+
+        class funclike:
+            # Has to be callable, and have correct
+            # __code__, __annotations__, __defaults__, and
+            # __kwdefaults__ attributes
+
+            def __init__(self, func):
+                self.__code__ = func.__code__
+                self.__annotations__ = func.__annotations__
+                self.__defaults__ = func.__defaults__
+                self.__kwdefaults__ = func.__kwdefaults__
+                self.func = func
+
+            def __call__(self, *args, **kwargs):
+                return self.func(*args, **kwargs)
+
+        sig_func = inspect.Signature.from_function(func)
+
+        sig_funclike = inspect.Signature.from_function(funclike(func))
+        self.assertEqual(sig_funclike, sig_func)
+
+        sig_funclike = inspect.signature(funclike(func))
+        self.assertEqual(sig_funclike, sig_func)
+
     def test_signature_on_method(self):
         class Test:
             def __init__(*args):