diff --git a/v2rayN/ServiceLib/Global.cs b/v2rayN/ServiceLib/Global.cs
index 92c50a37..2c3e44d0 100644
--- a/v2rayN/ServiceLib/Global.cs
+++ b/v2rayN/ServiceLib/Global.cs
@@ -757,15 +757,17 @@ public class Global
         "10.0.0.1/30",
     ];
 
+    // Prefixes must leave room for a peer address (max /126); the sing-box system
+    // stack derives a gateway from the first prefix and rejects single-address prefixes.
     public static readonly IReadOnlyList<string> TunIpv6Address =
     [
-        "fc00::172:18:0:1/128",
-        "fc00::172:31:0:1/128",
-        "fc00::172:20:0:1/128",
-        "fc00::172:16:0:1/128",
-        "fc00::192:168:100:1/128",
-        "fc00::10:10:14:1/128",
-        "fc00::10:1:0:1/128",
-        "fc00::10:0:0:1/128",
+        "fc00::172:18:0:1/126",
+        "fc00::172:31:0:1/126",
+        "fc00::172:20:0:1/126",
+        "fc00::172:16:0:1/126",
+        "fc00::192:168:100:1/126",
+        "fc00::10:10:14:1/126",
+        "fc00::10:1:0:1/126",
+        "fc00::10:0:0:1/126",
     ];
 }