Index: trunk/src/org/openstreetmap/josm/data/Preferences.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 10379)
+++ trunk/src/org/openstreetmap/josm/data/Preferences.java	(revision 10380)
@@ -507,14 +507,14 @@
      * @throws IOException if any I/O error occurs
      */
-    public void save() throws IOException {
+    public synchronized void save() throws IOException {
         save(getPreferenceFile(),
                 new FilteredCollection<>(settingsMap.entrySet(), NO_DEFAULT_SETTINGS_ENTRY), false);
     }
 
-    public void saveDefaults() throws IOException {
+    public synchronized void saveDefaults() throws IOException {
         save(getDefaultsCacheFile(), defaultsMap.entrySet(), true);
     }
 
-    public void save(File prefFile, Collection<Entry<String, Setting<?>>> settings, boolean defaults) throws IOException {
+    protected void save(File prefFile, Collection<Entry<String, Setting<?>>> settings, boolean defaults) throws IOException {
 
         if (!defaults) {