Index: applications/editors/josm/plugins/pdfimport/src/pdfimport/Preview.java
===================================================================
--- applications/editors/josm/plugins/pdfimport/src/pdfimport/Preview.java	(revision 34438)
+++ applications/editors/josm/plugins/pdfimport/src/pdfimport/Preview.java	(revision 34439)
@@ -19,9 +19,10 @@
 	public static FilePlacement placement;
 	
-	public static void set (@NotNull OsmDataLayer dataLayer, @NotNull FilePlacement placement) {
+	public static synchronized void set (@NotNull OsmDataLayer dataLayer, @NotNull FilePlacement placement) {
 		clear();
 		Preview.dataLayer = dataLayer;
 		Preview.placement = placement;
-		MainApplication.getLayerManager().addLayer(dataLayer);  
+		MainApplication.getLayerManager().addLayer(dataLayer); 
+
 	}