diff --git a/gramps/gui/widgets/fanchart.py b/gramps/gui/widgets/fanchart.py
index d3e612e05..a37a1f6a3 100644
--- a/gramps/gui/widgets/fanchart.py
+++ b/gramps/gui/widgets/fanchart.py
@@ -801,7 +801,7 @@ class FanChartBaseWidget(Gtk.DrawingArea):
         """
         return TYPE_BOX_NORMAL
 
-    def personpos_at_angle(generation, angledeg, btype):
+    def personpos_at_angle(self, generation, angledeg, btype):
         """
         returns the person in generation generation at angle of type btype.
         """