diff --git a/tools/lgdl.py b/tools/lgdl.py
index 38f3ffd..f2f5ed8 100644
--- a/tools/lgdl.py
+++ b/tools/lgdl.py
@@ -91,6 +91,8 @@ def sniff(data: bytes) -> str:
         return "epub/zip"
     if data[:8] == b"\xd0\xcf\x11\xe0\xa1\xb1\x1a\xe1":
         return "doc/ole"
+    if data[:8] in (b"AT&TFORM", b"AT&ToC\01", b"AT&ToC\02"):
+        return "djvu"
     if b"<html" in data[:2000].lower():
         return "HTML-ERROR"
     return "unknown"
@@ -123,8 +125,13 @@ def download(f_id, out_dir, name, tries=8):
             continue
         url = m.group(1)
         tmp = out + ".part"
-        rc = curl(url, out=tmp, referer=f"{BASE}/ads.php?md5={md5}", binary=True,
-                  timeout=900, extra=["-C", "-"])
+        try:
+            rc = curl(url, out=tmp, referer=f"{BASE}/ads.php?md5={md5}", binary=True,
+                      timeout=900, extra=["-C", "-"])
+        except RuntimeError as e:
+            print(f"  try {t}: fetch error ({e}) — back off")
+            time.sleep(45)
+            continue
         data = open(tmp, "rb").read()
         kind = sniff(data)
         ok_size = (size == 0) or (len(data) == size)