diff --git a/src/calibre/srv/http_response.py b/src/calibre/srv/http_response.py
index af9f8f6c92..f83dc87e82 100644
--- a/src/calibre/srv/http_response.py
+++ b/src/calibre/srv/http_response.py
@@ -178,7 +178,7 @@ def compress_readable_output(src_file, compress_level=6):
             prefix_written = True
             data = gzip_prefix() + data
         yield data
-    yield zobj.flush() + struct.pack(b"<L", crc) + struct.pack(b"<L", size)
+    yield zobj.flush() + struct.pack(b"<L", crc & 0xffffffff) + struct.pack(b"<L", size)
 # }}}