diff --git a/src/calibre/srv/loop.py b/src/calibre/srv/loop.py
index a82ffcce8e..531fc53602 100644
--- a/src/calibre/srv/loop.py
+++ b/src/calibre/srv/loop.py
@@ -145,7 +145,7 @@ def parse_trusted_ips(spec):
 
 
 def is_ip_trusted(remote_addr, trusted_ips):
-    remote_addr = getattr(remote_addr, 'ipv4_mapped', remote_addr)
+    remote_addr = getattr(remote_addr, 'ipv4_mapped', None) or remote_addr
     for tip in trusted_ips:
         if hasattr(tip, 'hosts'):
             if remote_addr in tip: