diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
--- a/Modules/_cursesmodule.c
+++ b/Modules/_cursesmodule.c
@@ -361,10 +361,17 @@ PyCurses_ConvertToString(PyCursesWindowO
 {
     if (PyUnicode_Check(obj)) {
 #ifdef HAVE_NCURSESW
+        Py_ssize_t wlen;
         assert (wstr != NULL);
-        *wstr = PyUnicode_AsWideCharString(obj, NULL);
+
+        *wstr = PyUnicode_AsWideCharString(obj, &wlen);
         if (*wstr == NULL)
             return 0;
+        if (wlen != wcslen(wstr)) {
+            PyErr_SetString(PyExc_TypeError,
+                            "embedded null character");
+            return 0;
+        }
         return 2;
 #else
         assert (wstr == NULL);
diff --git a/Modules/_localemodule.c b/Modules/_localemodule.c
--- a/Modules/_localemodule.c
+++ b/Modules/_localemodule.c
@@ -205,16 +205,27 @@ PyLocale_strcoll(PyObject* self, PyObjec
 {
     PyObject *os1, *os2, *result = NULL;
     wchar_t *ws1 = NULL, *ws2 = NULL;
+    Py_ssize_t wlen;
 
     if (!PyArg_ParseTuple(args, "UU:strcoll", &os1, &os2))
         return NULL;
     /* Convert the unicode strings to wchar[]. */
-    ws1 = PyUnicode_AsWideCharString(os1, NULL);
+    ws1 = PyUnicode_AsWideCharString(os1, &wlen);
     if (ws1 == NULL)
         goto done;
+    if (wlen != wcslen(ws1)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "embedded null character");
+        goto done;
+    }
     ws2 = PyUnicode_AsWideCharString(os2, NULL);
     if (ws2 == NULL)
         goto done;
+    if (wlen != wcslen(ws2)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "embedded null character");
+        goto done;
+    }
     /* Collate the strings. */
     result = PyLong_FromLong(wcscoll(ws1, ws2));
   done:
@@ -246,6 +257,11 @@ PyLocale_strxfrm(PyObject* self, PyObjec
     s = PyUnicode_AsWideCharString(str, &n1);
     if (s == NULL)
         goto exit;
+    if (n1 != wcslen(s)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "embedded null character");
+        goto exit;
+    }
 
     /* assume no change in size, first */
     n1 = n1 + 1;
diff --git a/Python/import.c b/Python/import.c
--- a/Python/import.c
+++ b/Python/import.c
@@ -4123,6 +4123,7 @@ NullImporter_init(NullImporter *self, Py
     PyObject *pathobj;
     DWORD rv;
     wchar_t *path;
+    Py_ssize_t len;
 
     if (!_PyArg_NoKeywords("NullImporter()", kwds))
         return -1;
@@ -4136,9 +4137,16 @@ NullImporter_init(NullImporter *self, Py
         return -1;
     }
 
-    path = PyUnicode_AsWideCharString(pathobj, NULL);
+    path = PyUnicode_AsWideCharString(pathobj, &len);
     if (path == NULL)
         return -1;
+    if (len != wcslen(path)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "embedded null character");
+        PyMem_Free(path);
+        return -1;
+    }
+
     /* see issue1293 and issue3677:
      * stat() on Windows doesn't recognise paths like
      * "e:\\shared\\" and "\\\\whiterab-c2znlh\\shared" as dirs.