Index: Lib/plistlib.py
===================================================================
--- Lib/plistlib.py	(revision 69418)
+++ Lib/plistlib.py	(working copy)
@@ -397,12 +397,15 @@
         self.root = None
 
     def parse(self, fileobj):
-        from xml.parsers.expat import ParserCreate
+        from xml.parsers.expat import ParserCreate, ExpatError
         parser = ParserCreate()
         parser.StartElementHandler = self.handleBeginElement
         parser.EndElementHandler = self.handleEndElement
         parser.CharacterDataHandler = self.handleData
-        parser.ParseFile(fileobj)
+        try:
+            parser.ParseFile(fileobj)
+        except ExpatError as ee:
+            raise ValueError("Invalid PropertyList content:\n %s" % ee)
         return self.root
 
     def handleBeginElement(self, element, attrs):
Index: Lib/test/test_plistlib.py
===================================================================
--- Lib/test/test_plistlib.py	(revision 69418)
+++ Lib/test/test_plistlib.py	(working copy)
@@ -183,7 +183,15 @@
         self.assertEqual(test1, result1)
         self.assertEqual(test2, result2)
 
-
+    def test_garbage(self):
+        pl = self._create()
+        data = plistlib.writePlistToString(pl)
+        from_str = plistlib.readPlistFromString
+        self.assertRaises(ValueError, from_str, data * 2)
+        self.assertRaises(ValueError, from_str, data[:100])
+        self.assertRaises(ValueError, from_str, "invalid" + data)
+        self.assertRaises(ValueError, from_str, data + "invalid")
+        
 def test_main():
     test_support.run_unittest(TestPlistlib)