Index: /trunk/src/org/openstreetmap/josm/actions/mapmode/ZoomAction.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/actions/mapmode/ZoomAction.java	(revision 16899)
+++ /trunk/src/org/openstreetmap/josm/actions/mapmode/ZoomAction.java	(revision 16900)
@@ -55,5 +55,11 @@
         if (r.width >= 3 && r.height >= 3 && MainApplication.isDisplayingMapView()) {
             MapView mv = MainApplication.getMap().mapView;
-            mv.zoomToFactor(mv.getEastNorth(r.x+r.width/2, r.y+r.height/2), r.getWidth()/mv.getWidth());
+            final double factor;
+            if (r.x == e.getPoint().x || r.y == e.getPoint().y) {
+                factor = mv.getWidth() / r.getWidth(); // zoom out
+            } else {
+                factor = r.getWidth() / mv.getWidth(); // zoom in
+            }
+            mv.zoomToFactor(mv.getEastNorth(r.x + r.width / 2, r.y + r.height / 2), factor);
         }
     }