diff --git a/cps/helper.py b/cps/helper.py
index 9871af0c..dce1a280 100644
--- a/cps/helper.py
+++ b/cps/helper.py
@@ -747,9 +747,10 @@ def get_book_cover(book_id, resolution=None):
     return get_book_cover_internal(book, use_generic_cover_on_failure=True, resolution=resolution)
 
 
-# Called only by kobo sync -> cover not found should be answered with 404 and not with default cover
-def get_book_cover_with_uuid(book_uuid, resolution=None):
+def get_book_cover_with_uuid(book_uuid, resolution=None, none_on_missing=False):
     book = calibre_db.get_book_by_uuid(book_uuid)
+    if not book and none_on_missing:
+        return  # allows kobo.HandleCoverImageRequest to proxy request
     return get_book_cover_internal(book, use_generic_cover_on_failure=False, resolution=resolution)
 
 
diff --git a/cps/kobo.py b/cps/kobo.py
index de5d3235..8afadafd 100644
--- a/cps/kobo.py
+++ b/cps/kobo.py
@@ -930,7 +930,10 @@ def get_current_bookmark_response(current_bookmark):
 @kobo.route("/<book_uuid>/<width>/<height>/<Quality>/<isGreyscale>/image.jpg")
 @requires_kobo_auth
 def HandleCoverImageRequest(book_uuid, width, height, Quality, isGreyscale):
-    book_cover = helper.get_book_cover_with_uuid(book_uuid, resolution=COVER_THUMBNAIL_SMALL)
+    book_cover = helper.get_book_cover_with_uuid(
+        book_uuid,
+        resolution=COVER_THUMBNAIL_SMALL,
+        none_on_missing=config.config_kobo_proxy)
     if not book_cover:
         if config.config_kobo_proxy:
             log.debug("Cover for unknown book: %s proxied to kobo" % book_uuid)
@@ -941,7 +944,7 @@ def HandleCoverImageRequest(book_uuid, width, height, Quality, isGreyscale):
         else:
             log.debug("Cover for unknown book: %s requested" % book_uuid)
             # additional proxy request make no sense, -> direct return
-            return make_response(jsonify({}))
+            return abort(404)
     log.debug("Cover request received for book %s" % book_uuid)
     return book_cover