diff --git a/wagtail/utils/widgets.py b/wagtail/utils/widgets.py
index 48070451d3..8ae51ce6b9 100644
--- a/wagtail/utils/widgets.py
+++ b/wagtail/utils/widgets.py
@@ -1,3 +1,5 @@
+from __future__ import absolute_import, unicode_literals
+
 from django.forms.widgets import Widget
 from django.utils.safestring import mark_safe
 
@@ -8,7 +10,7 @@ class WidgetWithScript(Widget):
 
         final_attrs = self.build_attrs(attrs, name=name)
         id_ = final_attrs.get('id', None)
-        if 'id_' is None:
+        if id_ is None:
             return widget
 
         js = self.render_js_init(id_, name, value)