diff --git a/skimage/viewer/qt.py b/skimage/viewer/qt.py
index 9a6537b3..b36c15dc 100644
--- a/skimage/viewer/qt.py
+++ b/skimage/viewer/qt.py
@@ -14,9 +14,11 @@ except ImportError:
             QWidget = object
 
         class QtCore(object):
-            def Signal(*args, **kwargs): pass
             Qt = object
 
+            def Signal(self, *args, **kwargs): 
+                pass
+
         QtWidgets = QtGui
 
         has_qt = False