diff --git a/Lib/test/test_plistlib.py b/Lib/test/test_plistlib.py
index bf745d3..8e8d3e3 100644
--- a/Lib/test/test_plistlib.py
+++ b/Lib/test/test_plistlib.py
@@ -165,13 +165,16 @@
         self.assertEqual(dict(pl), dict(pl2))
 
     def test_controlcharacters(self):
-        # chars in the range 0..31 are replaced by '?', except for
-        # \r, \n and \t since they aren't legal XML characters
-        testString = "".join([chr(i) for i in range(32)])
-        expectedResult = '?????????\t\n??\n??????????????????'
-        xml = plistlib.writePlistToString(testString)
-        result = plistlib.readPlistFromString(xml)
-        self.assertEqual(result, expectedResult)
+        for i in range(128):
+            c = chr(i)
+            testString = "string containing %s" % c
+            if i >= 32 or c in "\r\n\t":
+                # \r, \n and \t are the only legal control chars in XML
+                plistlib.writePlistToString(testString)
+            else:
+                self.assertRaises(ValueError,
+                                  plistlib.writePlistToString,
+                                  testString)
 
     def test_nondictroot(self):
         test1 = "abc"