diff -r d3cda8cf4d42 Objects/fileobject.c
--- a/Objects/fileobject.c	Mon Aug 17 22:10:47 2015 -0400
+++ b/Objects/fileobject.c	Tue Aug 18 14:22:46 2015 +0300
@@ -319,6 +319,7 @@
 open_the_file(PyFileObject *f, char *name, char *mode)
 {
     char *newmode;
+    int newmodelen;
     assert(f != NULL);
     assert(PyFile_Check(f));
 #ifdef MS_WINDOWS
@@ -331,7 +332,9 @@
     assert(f->f_fp == NULL);
 
     /* probably need to replace 'U' by 'rb' */
-    newmode = PyMem_MALLOC(strlen(mode) + 3);
+    newmodelen = strlen(mode) + 3;
+    newmode = PyMem_MALLOC(newmodelen);
+    memset(newmode, 0, newmodelen);
     if (!newmode) {
         PyErr_NoMemory();
         return NULL;