diff --git a/skimage/viewer/plugins/canny.py b/skimage/viewer/plugins/canny.py
index 176dcf0d..81cc07fe 100644
--- a/skimage/viewer/plugins/canny.py
+++ b/skimage/viewer/plugins/canny.py
@@ -18,3 +18,7 @@ class CannyPlugin(Plugin):
     def callback(self, *args, **kwargs):
         image = canny(*args, **kwargs)
         self.image_viewer.overlay = image
+
+    def closeEvent(self, event):
+        self.image_viewer.overlay = None
+        super(CannyPlugin, self).closeEvent(event)
diff --git a/skimage/viewer/viewers/core.py b/skimage/viewer/viewers/core.py
index a2bc2385..65939e9a 100644
--- a/skimage/viewer/viewers/core.py
+++ b/skimage/viewer/viewers/core.py
@@ -117,7 +117,10 @@ class ImageViewer(QtGui.QMainWindow):
     @overlay.setter
     def overlay(self, image):
         self._overlay = image
-        if self._overlay_plot is None:
+        if image is None:
+            self.ax.images.remove(self._overlay_plot)
+            self._overlay_plot = None
+        elif self._overlay_plot is None:
             self._overlay_plot = self.ax.imshow(image, cmap=self.overlay_cmap)
         else:
             self._overlay_plot.set_array(image)