diff --git a/SketchWidget.py b/SketchWidget.py
index a5aaf43..578f31f 100644
--- a/SketchWidget.py
+++ b/SketchWidget.py
@@ -20,6 +20,7 @@ class SketchWidget:
         self.line_width = 0.8
         self.axis_width = 1.8
         self.axis_length = 50
+        self.zoom_factor = 1.2
 
         try:
             # try double-buffered
@@ -217,14 +218,22 @@ class SketchWidget:
 
     def scroll_event(self, widget, event, data = None):
         if event.direction == gtk.gdk.SCROLL_UP:
-            self.view_center = self.screenPtToPt((event.x,
+            zoom_pt = self.screenPtToPt((event.x,
                 self.size[1] - event.y))
-            self.view_width /= 1.2
+            off_x = zoom_pt[0] - self.view_center[0]
+            off_y = zoom_pt[1] - self.view_center[1]
+            self.view_center = (zoom_pt[0] - off_x / self.zoom_factor,
+                    zoom_pt[1] - off_y / self.zoom_factor)
+            self.view_width /= self.zoom_factor
             self.redraw()
         elif event.direction == gtk.gdk.SCROLL_DOWN:
-            self.view_center = self.screenPtToPt((event.x,
+            zoom_pt = self.screenPtToPt((event.x,
                 self.size[1] - event.y))
-            self.view_width *= 1.2
+            off_x = zoom_pt[0] - self.view_center[0]
+            off_y = zoom_pt[1] - self.view_center[1]
+            self.view_center = (zoom_pt[0] - off_x * self.zoom_factor,
+                    zoom_pt[1] - off_y * self.zoom_factor)
+            self.view_width *= self.zoom_factor
             self.redraw()
 
     def redraw(self):