diff -r 6a2de662eeb7 Lib/test/test_long.py
--- a/Lib/test/test_long.py	Thu Jul 28 17:08:52 2016 +0200
+++ b/Lib/test/test_long.py	Thu Jul 28 18:15:05 2016 +0200
@@ -1102,6 +1102,7 @@
         self.assertEqual((-1).to_bytes(5, 'big', signed=True),
                          b'\xff\xff\xff\xff\xff')
         self.assertRaises(OverflowError, (1).to_bytes, 0, 'big')
+        self.assertRaises(OverflowError, (-1).to_bytes, 0, 'big', signed=True)
 
     def test_from_bytes(self):
         def check(tests, byteorder, signed=False):
diff -r 6a2de662eeb7 Objects/longobject.c
--- a/Objects/longobject.c	Thu Jul 28 17:08:52 2016 +0200
+++ b/Objects/longobject.c	Thu Jul 28 18:15:05 2016 +0200
@@ -5121,6 +5121,12 @@
         return NULL;
     }
 
+    /* Corner case: (-1).to_bytes(0, ...) should raise OverflowError. */
+    if (length == 0 && Py_SIZE(v) == -1) {
+        PyErr_SetString(PyExc_OverflowError, "int too big to convert");
+        return NULL;
+    }
+
     bytes = PyBytes_FromStringAndSize(NULL, length);
     if (bytes == NULL)
         return NULL;