diff --git a/GLViewer/NavigationControl.cpp b/GLViewer/NavigationControl.cpp
index 9134e8c0f24144d4ee34bbbc43275427ee7d1b8a..5af0978210a16c85fe63de25173dc3f2f4e7ec14 100644
--- a/GLViewer/NavigationControl.cpp
+++ b/GLViewer/NavigationControl.cpp
@@ -103,7 +103,11 @@ void GLViewer::NavigationControl::wheelEvent( double delta, QWheelEvent* evt )
 {
     GLViewer &v = *GetViewer();
 
-    delta *= -0.0005 * v.distToFocusPoint();
+    delta *= -0.0005;
+    if( delta < 0.0 )
+        delta = delta / (1.0-delta);
+
+    delta *= v.distToFocusPoint();
 
     if( v.distToFocusPoint() + delta > 0.0 )
         v.setDistToFocusPoint( v.distToFocusPoint() + delta );