Index: trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMSLayerPanel.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMSLayerPanel.java	(revision 13750)
+++ trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMSLayerPanel.java	(revision 13751)
@@ -148,4 +148,5 @@
         registerValidableComponent(rawUrl);
         registerValidableComponent(wmsUrl);
+        registerValidableComponent(setDefaultLayers);
     }
 
@@ -199,4 +200,7 @@
             return false;
         }
+        if (setDefaultLayers.isSelected() && (tree == null || tree.getSelectedLayers().isEmpty())) {
+            return false;
+        }
         if (endpoint.isSelected()) {
             return !getImageryRawUrl().isEmpty();
Index: trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMTSLayerPanel.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMTSLayerPanel.java	(revision 13750)
+++ trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMTSLayerPanel.java	(revision 13751)
@@ -62,4 +62,5 @@
         add(name, GBC.eol().fill(GBC.HORIZONTAL));
         registerValidableComponent(rawUrl);
+        registerValidableComponent(setDefaultLayer);
 
         getLayers.addActionListener(e -> {
@@ -116,5 +117,7 @@
     @Override
     protected boolean isImageryValid() {
-        return !getImageryName().isEmpty() && !getImageryRawUrl().isEmpty();
+        return ((setDefaultLayer.isSelected() && layerTable !=null && layerTable.getSelectedLayer() != null)
+                || !setDefaultLayer.isSelected()
+                ) &&  !getImageryName().isEmpty() && !getImageryRawUrl().isEmpty();
     }