Index: applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/MapillaryPlugin.java
===================================================================
--- applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/MapillaryPlugin.java	(revision 31826)
+++ applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/MapillaryPlugin.java	(revision 31827)
@@ -131,5 +131,5 @@
 
     if (Main.pref.get("mapillary.access-token") == null)
-      MapillaryUser.isTokenValid = false;
+      MapillaryUser.setTokenValid(false);
   }
 
Index: applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/oauth/MapillaryUser.java
===================================================================
--- applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/oauth/MapillaryUser.java	(revision 31826)
+++ applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/oauth/MapillaryUser.java	(revision 31827)
@@ -23,5 +23,5 @@
   private static String imagesHash;
   /** If the stored token is valid or not. */
-  public static boolean isTokenValid = true;
+  private static boolean isTokenValid = true;
 
   private MapillaryUser() {
@@ -82,5 +82,5 @@
    * Resets the MapillaryUser to null values.
    */
-  public static void reset() {
+  public static synchronized void reset() {
     username = null;
     imagesPolicy = null;
@@ -89,3 +89,7 @@
     Main.pref.put("mapillary.access-token", null);
   }
+
+  public static synchronized void setTokenValid(boolean value) {
+    isTokenValid = value;
+  }
 }
Index: applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/oauth/OAuthPortListener.java
===================================================================
--- applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/oauth/OAuthPortListener.java	(revision 31826)
+++ applications/editors/josm/plugins/mapillary/src/org/openstreetmap/josm/plugins/mapillary/oauth/OAuthPortListener.java	(revision 31827)
@@ -71,5 +71,5 @@
       Main.info("Successful login with Mapillary, the access token is: " + accessToken);
       // Saves the access token in preferences.
-      MapillaryUser.isTokenValid = true;
+      MapillaryUser.setTokenValid(true);
       if (Main.main != null) {
         Main.pref.put("mapillary.access-token", accessToken);