diff --git a/Products/LDAPMultiPlugins/CHANGES.txt b/Products/LDAPMultiPlugins/CHANGES.txt
index 89b31a7..127ae08 100644
--- a/Products/LDAPMultiPlugins/CHANGES.txt
+++ b/Products/LDAPMultiPlugins/CHANGES.txt
@@ -6,6 +6,10 @@ To see earlier changes please see HISTORY.txt.
 2.0 (unreleased)
 ----------------
 
+- Bug: Demangling user prefix could not deal with non-string user 
+  ids, which may appear in certain cases.
+  (https://bugs.launchpad.net/bugs/586931)
+
 - Bug: Added GenericSetup magic to fully provide the INode interface
   for the exporter and importer classes, making it easier to nest 
   within other importers.
diff --git a/Products/LDAPMultiPlugins/LDAPPluginBase.py b/Products/LDAPMultiPlugins/LDAPPluginBase.py
index 702f6e9..62971ab 100644
--- a/Products/LDAPMultiPlugins/LDAPPluginBase.py
+++ b/Products/LDAPMultiPlugins/LDAPPluginBase.py
@@ -153,6 +153,10 @@ class LDAPPluginBase(Folder, BasePlugin, Cacheable):
 
     security.declarePrivate('_demangle')
     def _demangle(self, princid):
+        # Sanity check
+        if not isinstance(princid, basestring):
+            return None
+
         # User must start with our prefix (which is likely to be blank anyway)
         if not princid.startswith(self.prefix):
             return None
diff --git a/Products/LDAPMultiPlugins/tests/test_LDAPMultiPlugins.py b/Products/LDAPMultiPlugins/tests/test_LDAPMultiPlugins.py
index 2572b77..fd7b54b 100644
--- a/Products/LDAPMultiPlugins/tests/test_LDAPMultiPlugins.py
+++ b/Products/LDAPMultiPlugins/tests/test_LDAPMultiPlugins.py
@@ -17,25 +17,26 @@ $Id$
 
 import unittest
 
-from Products.PluggableAuthService.interfaces.plugins import \
-     IUserEnumerationPlugin
-from Products.PluggableAuthService.interfaces.plugins import \
-    IGroupsPlugin
-from Products.PluggableAuthService.interfaces.plugins import \
-    IGroupEnumerationPlugin
-from Products.PluggableAuthService.interfaces.plugins import \
-    IRoleEnumerationPlugin
-
-from Products.LDAPMultiPlugins.interfaces import ILDAPMultiPlugin
-
 
 class LMPBaseTests(unittest.TestCase):
 
+    def _makeOne(self):
+        return self._getTargetClass()('testplugin')
+
     def _getTargetClass(self):
         from Products.LDAPMultiPlugins.LDAPPluginBase import LDAPPluginBase
         return LDAPPluginBase
 
     def test_interfaces(self):
+        from Products.LDAPMultiPlugins.interfaces import ILDAPMultiPlugin
+        from Products.PluggableAuthService.interfaces.plugins import \
+             IUserEnumerationPlugin
+        from Products.PluggableAuthService.interfaces.plugins import \
+            IGroupsPlugin
+        from Products.PluggableAuthService.interfaces.plugins import \
+            IGroupEnumerationPlugin
+        from Products.PluggableAuthService.interfaces.plugins import \
+            IRoleEnumerationPlugin
         from zope.interface.verify import verifyClass
 
         verifyClass(ILDAPMultiPlugin, self._getTargetClass())
@@ -45,6 +46,14 @@ class LMPBaseTests(unittest.TestCase):
         verifyClass(IGroupEnumerationPlugin, self._getTargetClass())
         verifyClass(IRoleEnumerationPlugin, self._getTargetClass())
 
+    def test_demangle_invalid_userid(self):
+        plugin = self._makeOne()
+        plugin.prefix = 'prefix_'
+
+        self.assertEquals(plugin._demangle(None), None)
+        self.assertEquals(plugin._demangle('incorrectprefix'), None)
+        self.assertEquals(plugin._demangle('prefix_user1'), 'user1')
+
 
 class ADMPTests(LMPBaseTests):