Index: trunk/src/org/openstreetmap/josm/io/session/SessionWriter.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/session/SessionWriter.java	(revision 17657)
+++ trunk/src/org/openstreetmap/josm/io/session/SessionWriter.java	(revision 17658)
@@ -12,4 +12,5 @@
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
@@ -271,5 +272,5 @@
         viewportEl.appendChild(scale);
         double dist100px = mapView.getDist100Pixel();
-        scale.setAttribute("meter-per-pixel", Double.toString(dist100px / 100));
+        scale.setAttribute("meter-per-pixel", String.format(Locale.ROOT, "%6f", dist100px / 100));
     }