Index: trunk/src/org/openstreetmap/josm/data/imagery/TMSCachedTileLoaderJob.java
===================================================================
--- trunk/src/org/openstreetmap/josm/data/imagery/TMSCachedTileLoaderJob.java	(revision 19652)
+++ trunk/src/org/openstreetmap/josm/data/imagery/TMSCachedTileLoaderJob.java	(revision 19653)
@@ -152,6 +152,8 @@
     private boolean isNotImage(Map<String, List<String>> headers, int statusCode) {
         if (statusCode == 200 && headers.containsKey("Content-Type") && !headers.get("Content-Type").isEmpty()) {
-            String contentType = headers.get("Content-Type").stream().findAny().orElse(null);
-            if (contentType != null && !contentType.startsWith("image") && !MVTFile.MIMETYPE.contains(contentType.toLowerCase(Locale.ROOT))) {
+            String contentType = headers.get("Content-Type").stream().findAny().orElse("").toLowerCase(Locale.ROOT);
+            if (!contentType.startsWith("image")
+                && !contentType.startsWith("application/octet-stream")
+                && !MVTFile.MIMETYPE.contains(contentType)) {
                 Logging.warn("Image not returned for tile: " + url + " content type was: " + contentType);
                 // not an image - do not store response in cache, so next time it will be queried again from the server