Index: src/zope/app/form/browser/tests/test_itemswidget.py
===================================================================
--- src/zope/app/form/browser/tests/test_itemswidget.py	(revision 73036)
+++ src/zope/app/form/browser/tests/test_itemswidget.py	(working copy)
@@ -130,6 +130,17 @@
     def test_not_required(self):
         self.failIf(self._makeWidget().required)
 
+    def test_toFieldValue(self):
+        widget = self._makeWidget()
+        self.assertEquals(
+            widget._toFieldValue(None), self._field.missing_value)
+        self.assertEquals(widget._toFieldValue('token1'), 'one')
+        self.assertRaises(
+            ConversionError, widget._toFieldValue, 'no_such_token')
+        self.assertRaises(
+            ConversionError, widget._toFieldValue, ['token1', 'token2'])
+
+
 class ItemsMultiDisplayWidgetTest(ItemsWidgetBaseTest):
     
     _widget = ItemsMultiDisplayWidget

Index: src/zope/app/form/browser/itemswidgets.py
===================================================================
--- src/zope/app/form/browser/itemswidgets.py	(revision 73036)
+++ src/zope/app/form/browser/itemswidgets.py	(working copy)
@@ -155,7 +155,7 @@
         if input:
             try:
                 return self.convertTokensToValues([input])[0]
-            except InvalidValue, e:
+            except (InvalidValue, TypeError), e:
                 raise ConversionError("Invalid value", e)
         else:
             return self.context.missing_value