diff -r 3811995aad73 Modules/_pickle.c
--- a/Modules/_pickle.c	Wed May 18 15:54:24 2016 -0700
+++ b/Modules/_pickle.c	Thu May 19 13:57:29 2016 +0200
@@ -1211,7 +1211,7 @@ static Py_ssize_t
    Returns -1 (with an exception set) on failure. On success, return the
    number of chars read. */
 static Py_ssize_t
-_Unpickler_Read(UnpicklerObject *self, char **s, Py_ssize_t n)
+_Unpickler_ReadImpl(UnpicklerObject *self, char **s, Py_ssize_t n)
 {
     Py_ssize_t num_read;
 
@@ -1243,6 +1243,14 @@ static Py_ssize_t
     return n;
 }
 
+#define _Unpickler_Read(self, s, n) \
+    ((self->next_read_idx <= PY_SSIZE_T_MAX - (n)          \
+      && self->next_read_idx + (n) <= self->input_len)     \
+     ? (*(s) = self->input_buffer + self->next_read_idx,   \
+        self->next_read_idx += (n),                        \
+        (n))                                               \
+     : _Unpickler_ReadImpl(self, (s), (n)))
+
 static Py_ssize_t
 _Unpickler_CopyLine(UnpicklerObject *self, char *line, Py_ssize_t len,
                     char **result)