diff --git a/OpenSim/Region/Environment/Modules/World/Terrain/PaintBrushes/RevertSphere.cs b/OpenSim/Region/Environment/Modules/World/Terrain/PaintBrushes/RevertSphere.cs
index 3deb458b81..db3fef71d4 100644
--- a/OpenSim/Region/Environment/Modules/World/Terrain/PaintBrushes/RevertSphere.cs
+++ b/OpenSim/Region/Environment/Modules/World/Terrain/PaintBrushes/RevertSphere.cs
@@ -72,7 +72,7 @@ namespace OpenSim.Region.Environment.Modules.World.Terrain.PaintBrushes
                     if (z > 0.0)
                     {
                         z *= duration;
-                        map[x, y] += (map[x, y] * (1.0 - z)) + (m_revertmap[x, y] * z);
+                        map[x, y] = (map[x, y] * (1.0 - z)) + (m_revertmap[x, y] * z);
                     }
                 }
             }
@@ -80,4 +80,4 @@ namespace OpenSim.Region.Environment.Modules.World.Terrain.PaintBrushes
 
         #endregion
     }
-}
\ No newline at end of file
+}