diff --git a/SketchWidget.py b/SketchWidget.py
index befc84c..bd9f2d3 100644
--- a/SketchWidget.py
+++ b/SketchWidget.py
@@ -210,10 +210,11 @@ class SketchWidget:
         if self.panning:
             start_pt = self.screenPtToPt(self.panning_start)
             this_pt = self.screenPtToPt((event.x, self.size[1] - event.y))
-            self.view_center = (self.view_center[0] + this_pt[0] - start_pt[0],
-                    self.view_center[1] + this_pt[1] - start_pt[1])
+            self.view_center = (self.view_center[0] - this_pt[0] + start_pt[0],
+                    self.view_center[1] - this_pt[1] + start_pt[1])
             self.panning_start = (event.x, self.size[1] - event.y)
-            self.widget.queue_draw_area(0, 0, self.size[0], self.size[1])
+            self.widget.queue_draw_area(0, 0,
+                    int(self.size[0]), int(self.size[1]))
 
     def scroll_event(self, widget, event, data = None):
         if event.direction == gtk.gdk.SCROLL_UP: