diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index e3880f55..1166b3b6 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -23,6 +23,8 @@ except ImportError:
             def Signal(self, *args, **kwargs): 
                 pass
 
+            QWidget = object
+
         QtCore = QtWidgets = QtCore_cls()
 
         has_qt = False