Index: Doc/library/os.rst
===================================================================
--- Doc/library/os.rst	(revision 68535)
+++ Doc/library/os.rst	(working copy)
@@ -202,8 +202,9 @@
 
    Set the environment variable named *varname* to the string *value*.  Such
    changes to the environment affect subprocesses started with :func:`os.system`,
-   :func:`popen` or :func:`fork` and :func:`execv`. Availability: most flavors of
-   Unix, Windows.
+   :func:`popen` or :func:`fork` and :func:`execv`.  Raises :exc:`ValueError`
+   if *varname* contains an '=' character.
+   Availability: most flavors of Unix, Windows.
 
    .. note::
 
@@ -317,7 +318,9 @@
 
    Unset (delete) the environment variable named *varname*. Such changes to the
    environment affect subprocesses started with :func:`os.system`, :func:`popen` or
-   :func:`fork` and :func:`execv`. Availability: most flavors of Unix, Windows.
+   :func:`fork` and :func:`execv`. Raises :exc:`OSError` if *varname* is
+   invalid, for example if it contains an '=' character.
+   Availability: most flavors of Unix, Windows.
 
    When :func:`unsetenv` is supported, deletion of items in ``os.environ`` is
    automatically translated into a corresponding call to :func:`unsetenv`; however,
Index: Lib/test/test_posix.py
===================================================================
--- Lib/test/test_posix.py	(revision 68535)
+++ Lib/test/test_posix.py	(working copy)
@@ -215,6 +215,23 @@
             self.assertEqual(type(k), str)
             self.assertEqual(type(v), str)
 
+    def test_putenv(self):
+        if hasattr(posix, 'putenv'):
+            posix.putenv("TESTTEST", "test")
+            posix.putenv("TESTTEST", "newvalue")
+            self.assertRaises(ValueError, posix.putenv, "FOO=BAR", "value")
+
+    def test_unsetenv(self):
+        if hasattr(posix, 'unsetenv'):
+            posix.putenv("TESTTEST", "test")
+            posix.unsetenv("TESTTEST")
+            posix.unsetenv("TESTTEST")
+            posix.unsetenv("BLAHBLAH")
+            posix.unsetenv("BLAHBLAH")
+            # POSIX requires unsetenv to fail here; the posix module
+            # originally didn't check the return value.
+            self.assertRaises(OSError, posix.unsetenv, "BAR=BAZ")
+
     def test_getcwd_long_pathnames(self):
         if hasattr(posix, 'getcwd'):
             dirname = 'getcwd-test-directory-0123456789abcdef-01234567890abcdef'
Index: Modules/posixmodule.c
===================================================================
--- Modules/posixmodule.c	(revision 68535)
+++ Modules/posixmodule.c	(working copy)
@@ -5174,12 +5174,19 @@
 	/* len includes space for a trailing \0; the size arg to
 	   PyBytes_FromStringAndSize does not count that */
 #ifdef MS_WINDOWS
-	len = wcslen(s1) + wcslen(s2) + 2;
-	newstr = PyUnicode_FromUnicode(NULL, (int)len - 1);
+	if (wcschr(s1, L'=') == NULL) {
+		len = wcslen(s1) + wcslen(s2) + 2;
+		newstr = PyUnicode_FromUnicode(NULL, (int)len - 1);
 #else
-	len = strlen(s1) + strlen(s2) + 2;
-	newstr = PyBytes_FromStringAndSize(NULL, (int)len - 1);
+	if (strchr(s1, '=') == NULL) {
+		len = strlen(s1) + strlen(s2) + 2;
+		newstr = PyBytes_FromStringAndSize(NULL, (int)len - 1);
 #endif
+	} else {
+		PyErr_SetString(PyExc_ValueError, "environment variable names "
+				"may not contain the '=' character");
+		return NULL;
+	}
 	if (newstr == NULL)
 		return PyErr_NoMemory();
 #ifdef MS_WINDOWS
@@ -5233,7 +5240,8 @@
 	if (!PyArg_ParseTuple(args, "s:unsetenv", &s1))
 		return NULL;
 
-	unsetenv(s1);
+	if (unsetenv(s1))
+		return posix_error();
 
 	/* Remove the key from posix_putenv_garbage;
 	 * this will cause it to be collected.  This has to