diff --git a/skimage/viewer/qt/QtCore.py b/skimage/viewer/qt/QtCore.py
index 897b8760..e0aa923a 100644
--- a/skimage/viewer/qt/QtCore.py
+++ b/skimage/viewer/qt/QtCore.py
@@ -7,3 +7,5 @@ elif qt_api == 'pyqt':
 else:
     # Mock objects
     Qt = None
+    def pyqtSignal(*args, **kwargs):
+        pass