Index: trunk/src/org/openstreetmap/josm/tools/ImageResource.java
===================================================================
--- trunk/src/org/openstreetmap/josm/tools/ImageResource.java	(revision 16073)
+++ trunk/src/org/openstreetmap/josm/tools/ImageResource.java	(revision 16074)
@@ -5,7 +5,7 @@
 import java.awt.Image;
 import java.awt.image.BufferedImage;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
 
 import javax.swing.AbstractAction;
@@ -31,5 +31,5 @@
      * Caches the image data for resized versions of the same image.
      */
-    private final Map<Dimension, BufferedImage> imgCache = new HashMap<>(4);
+    private final Map<Dimension, BufferedImage> imgCache = new ConcurrentHashMap<>(4);
     /**
      * SVG diagram information in case of SVG vector image.
@@ -285,6 +285,9 @@
     public ImageIcon getPaddedIcon(Dimension iconSize) {
         final Dimension cacheKey = new Dimension(-iconSize.width, -iconSize.height); // use negative width/height for differentiation
-        final BufferedImage image = imgCache.computeIfAbsent(cacheKey, ignore ->
-                ImageProvider.createPaddedIcon(getImageIcon().getImage(), iconSize));
+        BufferedImage image = imgCache.get(cacheKey);
+        if (image == null) {
+            image = ImageProvider.createPaddedIcon(getImageIcon().getImage(), iconSize);
+            imgCache.put(cacheKey, image);
+        }
         return new ImageIcon(image);
     }