Index: /trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMTSLayerPanel.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMTSLayerPanel.java	(revision 9681)
+++ /trunk/src/org/openstreetmap/josm/gui/preferences/imagery/AddWMTSLayerPanel.java	(revision 9682)
@@ -4,8 +4,11 @@
 import static org.openstreetmap.josm.tools.I18n.tr;
 
+import java.io.IOException;
+
 import javax.swing.JLabel;
 
 import org.openstreetmap.josm.data.imagery.ImageryInfo;
 import org.openstreetmap.josm.data.imagery.ImageryInfo.ImageryType;
+import org.openstreetmap.josm.data.imagery.WMTSTileSource;
 import org.openstreetmap.josm.tools.GBC;
 
@@ -32,5 +35,12 @@
     @Override
     protected ImageryInfo getImageryInfo() {
-        return new ImageryInfo(getImageryName(), "wmts:" + sanitize(getImageryRawUrl(), ImageryType.WMTS));
+        ImageryInfo ret = new ImageryInfo(getImageryName(), "wmts:" + sanitize(getImageryRawUrl(), ImageryType.WMTS));
+        try {
+            new WMTSTileSource(ret); // check if constructor throws an error
+        } catch (IOException e) {
+            throw new IllegalArgumentException(e); // if so, wrap exception, so proper message will be shown to the user
+        }
+        return ret;
+
     }