diff -r 41a99a2a7198 Objects/bufferobject.c
--- a/Objects/bufferobject.c	Sat Dec 24 10:41:37 2016 +0000
+++ b/Objects/bufferobject.c	Mon Dec 26 15:11:48 2016 -0500
@@ -500,14 +500,14 @@
     void *p;
     Py_ssize_t size;
 
-    if (!get_buf(self, &p, &size, ANY_BUFFER))
-        return NULL;
     if (PyIndex_Check(item)) {
         Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
         if (i == -1 && PyErr_Occurred())
             return NULL;
         if (i < 0)
             i += size;
+        if (!get_buf(self, &p, &size, ANY_BUFFER))
+            return NULL;
         return buffer_item(self, i);
     }
     else if (PySlice_Check(item)) {
@@ -518,6 +518,8 @@
             return NULL;
         }
 
+        if (!get_buf(self, &p, &size, ANY_BUFFER))
+            return NULL;
         if (slicelength <= 0)
             return PyString_FromStringAndSize("", 0);
         else if (step == 1)