diff -r f44f5daff665 Lib/test/test_sys.py
--- a/Lib/test/test_sys.py	Sun Aug 17 15:32:42 2014 +0300
+++ b/Lib/test/test_sys.py	Sun Aug 17 16:43:39 2014 +0300
@@ -770,6 +770,19 @@
         # but lists are
         self.assertEqual(sys.getsizeof([]), vsize('Pn') + gc_header_size)
 
+    def test_overflow(self):
+        class Overflow(int):
+            def __sizeof__(self):
+                return int(self)
+        self.assertEqual(sys.getsizeof(Overflow(sys.maxsize)),
+                         sys.maxsize + self.gc_headsize)
+        with self.assertRaises(OverflowError):
+            sys.getsizeof(Overflow(sys.maxsize + 1))
+        with self.assertRaises(ValueError):
+            sys.getsizeof(Overflow(-1))
+        with self.assertRaises((ValueError, OverflowError)):
+            sys.getsizeof(Overflow(-sys.maxsize - 1))
+
     def test_default(self):
         size = test.support.calcvobjsize
         self.assertEqual(sys.getsizeof(True), size('') + self.longdigit)
diff -r f44f5daff665 Python/sysmodule.c
--- a/Python/sysmodule.c	Sun Aug 17 15:32:42 2014 +0300
+++ b/Python/sysmodule.c	Sun Aug 17 16:43:39 2014 +0300
@@ -868,7 +868,7 @@
 {
     PyObject *res = NULL;
     PyObject *method;
-    size_t size;
+    Py_ssize_t size;
 
     /* Make sure the type is initialized. float gets initialized late */
     if (PyType_Ready(Py_TYPE(o)) < 0)
@@ -889,15 +889,20 @@
     if (res == NULL)
         return (size_t)-1;
 
-    size = PyLong_AsSize_t(res);
+    size = PyLong_AsSsize_t(res);
     Py_DECREF(res);
-    if (size == (size_t)-1 && PyErr_Occurred())
+    if (size == -1 && PyErr_Occurred())
         return (size_t)-1;
 
+    if (size < 0) {
+        PyErr_SetString(PyExc_ValueError, "negative size");
+        return (size_t)-1;
+    }
+
     /* add gc_head size */
     if (PyObject_IS_GC(o))
-        size += sizeof(PyGC_Head);
-    return size;
+        return ((size_t)size) + sizeof(PyGC_Head);
+    return (size_t)size;
 }
 
 static PyObject *