diff --git a/IPython/html/widgets/interaction.py b/IPython/html/widgets/interaction.py
index 25594e5..9bb060f 100644
--- a/IPython/html/widgets/interaction.py
+++ b/IPython/html/widgets/interaction.py
@@ -114,7 +114,7 @@ def _widget_from_abbrev(abbrev):
     
     widget = _widget_abbrev(abbrev)
     if widget is None:
-        raise ValueError("%r cannot be transformed to a Widget" % abbrev)
+        raise ValueError("%r cannot be transformed to a Widget" % (abbrev,))
     return widget
 
 def _yield_abbreviations_for_parameter(param, kwargs):