diff --git a/vtm/src/org/oscim/map/Viewport.java b/vtm/src/org/oscim/map/Viewport.java
index 126c0481..b42f39a4 100644
--- a/vtm/src/org/oscim/map/Viewport.java
+++ b/vtm/src/org/oscim/map/Viewport.java
@@ -1,6 +1,7 @@
 /*
  * Copyright 2012 Hannes Janetzek
  * Copyright 2016 devemux86
+ * Copyright 2016 Erik Duisters
  *
  * This file is part of the OpenScienceMap project (http://www.opensciencemap.org).
  *
@@ -389,6 +390,8 @@ public class Viewport {
     }
 
     protected boolean copy(Viewport viewport) {
+        boolean sizeChanged = mHeight != viewport.mHeight || mWidth != viewport.mWidth;
+
         mHeight = viewport.mHeight;
         mWidth = viewport.mWidth;
         mProjMatrix.copy(viewport.mProjMatrix);
@@ -399,7 +402,7 @@ public class Viewport {
         mRotationMatrix.copy(viewport.mRotationMatrix);
         mViewMatrix.copy(viewport.mViewMatrix);
         mViewProjMatrix.copy(viewport.mViewProjMatrix);
-        return viewport.getMapPosition(mPos);
+        return viewport.getMapPosition(mPos) || sizeChanged;
     }
 
     public double getMaxScale() {