diff --git a/tools/lib/url_file.py b/tools/lib/url_file.py
index 8ad2f96b3a..1e94a588f1 100644
--- a/tools/lib/url_file.py
+++ b/tools/lib/url_file.py
@@ -87,6 +87,7 @@ class URLFile:
 
     file_begin = self._pos
     file_end = self._pos + ll if ll is not None else self.get_length()
+    assert file_end != -1, f"Remote file is empty or doesn't exist: {self._url}"
     #  We have to align with chunks we store. Position is the begginiing of the latest chunk that starts before or at our file
     position = (file_begin // CHUNK_SIZE) * CHUNK_SIZE
     response = b""