Index: trunk/src/org/openstreetmap/josm/data/AutosaveTask.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/AutosaveTask.java	(revision 9584)
+++ trunk/src/org/openstreetmap/josm/data/AutosaveTask.java	(revision 9586)
@@ -159,5 +159,5 @@
             String filename = String.format("%1$s_%2$tY%2$tm%2$td_%2$tH%2$tM%2$tS%2$tL%3$s",
                     layer.layerFileName, now, index == 0 ? "" : '_' + index);
-            File result = new File(autosaveDir, filename+".osm");
+            File result = new File(autosaveDir, filename + "." + Main.pref.get("autosave.extension", "osm"));
             try {
                 if (result.createNewFile()) {