diff -r 4a6b8f86b081 Lib/test/test_tcl.py
--- a/Lib/test/test_tcl.py	Mon Apr 15 23:14:55 2013 -0700
+++ b/Lib/test/test_tcl.py	Tue Apr 16 10:06:44 2013 +0300
@@ -3,6 +3,7 @@
 import unittest
 import sys
 import os
+import _testcapi
 from test import support
 
 # Skip this test if the _tkinter module wasn't built.
@@ -176,8 +177,21 @@
         self.assertEqual(passValue((1, '2', (3.4,))), (1, '2', (3.4,)))
 
 
+class BigmemTclTest(unittest.TestCase):
+
+    def setUp(self):
+        self.interp = Tcl()
+
+    @unittest.skipUnless(_testcapi.INT_MAX < _testcapi.PY_SSIZE_T_MAX,
+                         "needs UINT_MAX < SIZE_MAX")
+    @support.bigmemtest(size=_testcapi.INT_MAX + 1, memuse=5, dry_run=False)
+    def test_huge_string(self, size):
+        value = ' ' * size
+        self.assertRaises(OverflowError, self.interp.call, 'set', '_', value)
+
+
 def test_main():
-    support.run_unittest(TclTest, TkinterTest)
+    support.run_unittest(TclTest, TkinterTest, BigmemTclTest)
 
 if __name__ == "__main__":
     test_main()
diff -r 4a6b8f86b081 Modules/_tkinter.c
--- a/Modules/_tkinter.c	Mon Apr 15 23:14:55 2013 -0700
+++ b/Modules/_tkinter.c	Tue Apr 16 10:06:44 2013 +0300
@@ -831,12 +831,18 @@
     else if (PyFloat_Check(value))
         return Tcl_NewDoubleObj(PyFloat_AS_DOUBLE(value));
     else if (PyTuple_Check(value)) {
-        Tcl_Obj **argv = (Tcl_Obj**)
-            ckalloc(PyTuple_Size(value)*sizeof(Tcl_Obj*));
-        int i;
+        Tcl_Obj **argv;
+        Py_ssize_t size, i;
+
+        size = PyTuple_Size(value);
+        if (size > INT_MAX || size > UINT_MAX / sizeof(Tcl_Obj *)) {
+            PyErr_SetString(PyExc_OverflowError, "tuple is too long");
+            return NULL;
+        }
+        argv = (Tcl_Obj **) ckalloc(((size_t)size) * sizeof(Tcl_Obj *));
         if(!argv)
           return 0;
-        for(i=0;i<PyTuple_Size(value);i++)
+        for (i = 0; i < size; i++)
           argv[i] = AsObj(PyTuple_GetItem(value,i));
         result = Tcl_NewListObj(PyTuple_Size(value), argv);
         ckfree(FREECAST argv);
@@ -855,6 +861,10 @@
 
         inbuf = PyUnicode_DATA(value);
         size = PyUnicode_GET_LENGTH(value);
+        if (size > INT_MAX || size > UINT_MAX / sizeof(Tcl_UniChar)) {
+            PyErr_SetString(PyExc_OverflowError, "string is too long");
+            return NULL;
+        }
         kind = PyUnicode_KIND(value);
         allocsize = ((size_t)size) * sizeof(Tcl_UniChar);
         outbuf = (Tcl_UniChar*)ckalloc(allocsize);
@@ -1010,7 +1020,7 @@
 Tkapp_CallArgs(PyObject *args, Tcl_Obj** objStore, int *pobjc)
 {
     Tcl_Obj **objv = objStore;
-    int objc = 0, i;
+    Py_ssize_t objc = 0, i;
     if (args == NULL)
         /* do nothing */;
 
@@ -1025,7 +1035,11 @@
         objc = PyTuple_Size(args);
 
         if (objc > ARGSZ) {
-            objv = (Tcl_Obj **)ckalloc(objc * sizeof(char *));
+            if (objc > INT_MAX || objc > UINT_MAX / sizeof(Tcl_Obj *)) {
+                PyErr_SetString(PyExc_OverflowError, "tuple is too long");
+                return NULL;
+            }
+            objv = (Tcl_Obj **)ckalloc(((size_t)objc) * sizeof(Tcl_Obj *));
             if (objv == NULL) {
                 PyErr_NoMemory();
                 objc = 0;