Index: /trunk/src/org/openstreetmap/josm/io/CachedFile.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/io/CachedFile.java	(revision 10685)
+++ /trunk/src/org/openstreetmap/josm/io/CachedFile.java	(revision 10686)
@@ -482,4 +482,6 @@
                         Arrays.asList(Long.toString(System.currentTimeMillis()), localPathEntry.get(1)));
                 return localFile;
+            } else if (con.getResponseCode() == HttpURLConnection.HTTP_NOT_FOUND) {
+                throw new IOException(tr("The requested URL {0} was not found", urlStr));
             }
             try (InputStream bis = new BufferedInputStream(con.getContent())) {