diff -r 76713f4d9f0f Lib/test/test_tcl.py
--- a/Lib/test/test_tcl.py	Sun Feb 09 06:07:47 2014 -0800
+++ b/Lib/test/test_tcl.py	Sun Feb 09 22:27:16 2014 +0200
@@ -341,7 +341,12 @@
         self.assertEqual(passValue(True), True if self.wantobjects else '1')
         self.assertEqual(passValue(False), False if self.wantobjects else '0')
         self.assertEqual(passValue('string'), 'string')
+        self.assertEqual(passValue('string\xbd'), 'string\xbd')
         self.assertEqual(passValue('string\u20ac'), 'string\u20ac')
+        self.assertEqual(passValue(b'string'), 'string')
+        self.assertEqual(passValue(b'string\xe2\x82\xac'), 'string\u20ac')
+        self.assertEqual(passValue('string\ud801'), 'string\ud801')
+        self.assertEqual(passValue('string\ud801\udca2'), 'string\ud801\udca2')
         self.assertEqual(passValue('str\x00ing'), 'str\x00ing')
         self.assertEqual(passValue('str\x00ing\xbd'), 'str\x00ing\xbd')
         self.assertEqual(passValue('str\x00ing\u20ac'), 'str\x00ing\u20ac')
@@ -397,6 +402,12 @@
         check('string\u20ac', 'string\u20ac')
         check(b'string', 'string')
         check(b'string\xe2\x82\xac', 'string\u20ac')
+        check('string\udca2', 'string\udced\udcb2\udca2')
+        check('string\ud801\udca2',
+              'string\udced\udca0\udc81\udced\udcb2\udca2')
+        check(b'string\xed\xa0\x81', 'string\udced\udca0\udc81')
+        check(b'string\xed\xa0\x81\xed\xb2\xa2',
+              'string\udced\udca0\udc81\udced\udcb2\udca2')
         check('str\x00ing', 'str\x00ing')
         check('str\x00ing\xbd', 'str\x00ing\xbd')
         check('str\x00ing\u20ac', 'str\x00ing\u20ac')
diff -r 76713f4d9f0f Modules/_tkinter.c
--- a/Modules/_tkinter.c	Sun Feb 09 06:07:47 2014 -0800
+++ b/Modules/_tkinter.c	Sun Feb 09 22:27:16 2014 +0200
@@ -329,16 +329,16 @@
 
 
 static PyObject *
-unicodeFromTclStringAndSize(const char *s, Py_ssize_t size)
+unicodeFromTclStringAndSize(const char *s, Py_ssize_t size, const char *errors)
 {
     PyObject *r = PyUnicode_DecodeUTF8(s, size, NULL);
     if (!r && PyErr_ExceptionMatches(PyExc_UnicodeDecodeError)) {
+        char *buf = NULL;
+        PyErr_Clear();
         /* Tcl encodes null character as \xc0\x80 */
         if (memchr(s, '\xc0', size)) {
-            char *buf, *q;
             const char *e = s + size;
-            PyErr_Clear();
-            q = buf = (char *)PyMem_Malloc(size);
+            char *q = buf = (char *)PyMem_Malloc(size);
             if (buf == NULL)
                 return NULL;
             while (s != e) {
@@ -351,9 +351,10 @@
             }
             s = buf;
             size = q - s;
-            r = PyUnicode_DecodeUTF8(s, size, NULL);
+        }
+        r = PyUnicode_DecodeUTF8(s, size, errors);
+        if (buf != NULL)
             PyMem_Free(buf);
-        }
     }
     return r;
 }
@@ -361,7 +362,7 @@
 static PyObject *
 unicodeFromTclString(const char *s)
 {
-    return unicodeFromTclStringAndSize(s, strlen(s));
+    return unicodeFromTclStringAndSize(s, strlen(s), NULL);
 }
 
 static PyObject *
@@ -369,7 +370,7 @@
 {
     int len;
     char *s = Tcl_GetStringFromObj(value, &len);
-    return unicodeFromTclStringAndSize(s, len);
+    return unicodeFromTclStringAndSize(s, len, NULL);
 }
 
 
@@ -970,7 +971,7 @@
     TkappObject *app = (TkappObject*)tkapp;
 
     if (value->typePtr == NULL) {
-        return unicodeFromTclStringAndSize(value->bytes, value->length);
+        return unicodeFromTclStringAndSize(value->bytes, value->length, NULL);
     }
 
     if (value->typePtr == app->BooleanType) {
@@ -1946,7 +1947,9 @@
         return PythonCmd_Error(interp);
 
     for (i = 0; i < (argc - 1); i++) {
-        PyObject *s = unicodeFromTclString(argv[i + 1]);
+        PyObject *s = unicodeFromTclStringAndSize(argv[i + 1],
+                                                  strlen(argv[i + 1]),
+                                                  "surrogateescape");
         if (!s || PyTuple_SetItem(arg, i, s)) {
             Py_DECREF(arg);
             return PythonCmd_Error(interp);