diff --git a/skimage/viewer/plugins/base.py b/skimage/viewer/plugins/base.py
index 749d5741..d9649b22 100644
--- a/skimage/viewer/plugins/base.py
+++ b/skimage/viewer/plugins/base.py
@@ -110,7 +110,7 @@ class Plugin(QtGui.QDialog):
         self.layout.addWidget(widget, self.row, 0)
         self.row += 1
 
-    def __iadd__(self, widget):
+    def __add__(self, widget):
         self.add_widget(widget)
         return self
 
diff --git a/skimage/viewer/viewers/core.py b/skimage/viewer/viewers/core.py
index fe22d750..3fd9724e 100644
--- a/skimage/viewer/viewers/core.py
+++ b/skimage/viewer/viewers/core.py
@@ -96,7 +96,7 @@ class ImageViewer(QtGui.QMainWindow):
 
         self.connect_event('motion_notify_event', self.update_status_bar)
 
-    def __iadd__(self, plugin):
+    def __add__(self, plugin):
         plugin.attach(self)
         return self