diff -r 908b801f8a62 Objects/longobject.c
--- a/Objects/longobject.c	Fri Jul 01 12:33:25 2016 +0300
+++ b/Objects/longobject.c	Sat Jul 02 11:09:35 2016 +0300
@@ -314,7 +314,6 @@
     v = _PyLong_New(ndigits);
     if (v != NULL) {
         digit *p = v->ob_digit;
-        Py_SIZE(v) = ndigits;
         while (ival) {
             *p++ = (digit)(ival & PyLong_MASK);
             ival >>= PyLong_SHIFT;
@@ -1079,7 +1078,8 @@
     v = _PyLong_New(ndigits);
     if (v != NULL) {
         digit *p = v->ob_digit;
-        Py_SIZE(v) = negative ? -ndigits : ndigits;
+        if (negative)
+            Py_SIZE(v) = -ndigits;
         t = abs_ival;
         while (t) {
             *p++ = (digit)(t & PyLong_MASK);
@@ -1109,7 +1109,6 @@
     v = _PyLong_New(ndigits);
     if (v != NULL) {
         digit *p = v->ob_digit;
-        Py_SIZE(v) = ndigits;
         while (ival) {
             *p++ = (digit)(ival & PyLong_MASK);
             ival >>= PyLong_SHIFT;
@@ -1148,7 +1147,8 @@
     v = _PyLong_New(ndigits);
     if (v != NULL) {
         digit *p = v->ob_digit;
-        Py_SIZE(v) = negative ? -ndigits : ndigits;
+        if (negative)
+            Py_SIZE(v) = -ndigits;
         t = abs_ival;
         while (t) {
             *p++ = (digit)(t & PyLong_MASK);
@@ -1178,7 +1178,6 @@
     v = _PyLong_New(ndigits);
     if (v != NULL) {
         digit *p = v->ob_digit;
-        Py_SIZE(v) = ndigits;
         while (ival) {
             *p++ = (digit)(ival & PyLong_MASK);
             ival >>= PyLong_SHIFT;
diff -r 908b801f8a62 Python/marshal.c
--- a/Python/marshal.c	Fri Jul 01 12:33:25 2016 +0300
+++ b/Python/marshal.c	Sat Jul 02 11:09:35 2016 +0300
@@ -802,7 +802,8 @@
     if (ob == NULL)
         return NULL;
 
-    Py_SIZE(ob) = n > 0 ? size : -size;
+    if (n <= 0)
+        Py_SIZE(ob) = -size;
 
     for (i = 0; i < size-1; i++) {
         d = 0;