diff --git a/v2rayN/ServiceLib.Tests/CoreConfig/V2ray/CoreConfigV2rayServiceTests.cs b/v2rayN/ServiceLib.Tests/CoreConfig/V2ray/CoreConfigV2rayServiceTests.cs
index 06bd472b..f9c4ddea 100644
--- a/v2rayN/ServiceLib.Tests/CoreConfig/V2ray/CoreConfigV2rayServiceTests.cs
+++ b/v2rayN/ServiceLib.Tests/CoreConfig/V2ray/CoreConfigV2rayServiceTests.cs
@@ -2,6 +2,38 @@ namespace ServiceLib.Tests.CoreConfig.V2ray;
 
 public class CoreConfigV2rayServiceTests
 {
+    [Test]
+    [Arguments("demo-seed", "srtp", 2)]
+    [Arguments(null, "srtp", 2)]
+    [Arguments("demo-seed", "none", 1)]
+    [Arguments(null, "none", 1)]
+    public async Task GenerateClientConfigContent_KcpHeader_ShouldPreserveInnerMask(string? seed, string header, int expectedCount)
+    {
+        var config = CoreConfigTestFactory.CreateConfig(ECoreType.Xray);
+        CoreConfigTestFactory.BindAppManagerConfig(config);
+        var node = CoreConfigTestFactory.CreateVmessNode(ECoreType.Xray);
+        node.Network = nameof(ETransport.kcp);
+        node.SetTransportExtra(new TransportExtraItem { KcpSeed = seed, KcpHeaderType = header });
+        var context = CoreConfigTestFactory.CreateContext(config, node, ECoreType.Xray);
+
+        var result = new CoreConfigV2rayService(context).GenerateClientConfigContent();
+
+        await result.Success.Should().BeTrue();
+        var generatedConfig = JsonNode.Parse(result.Data!.ToString()!)!;
+        var proxy = generatedConfig["outbounds"]!.AsArray()
+            .First(outbound => outbound!["tag"]!.GetValue<string>() == Global.ProxyTag)!;
+        var masks = proxy["streamSettings"]!["finalmask"]!["udp"]!.AsArray();
+        await masks.Count.Should().BeEqualTo(expectedCount);
+        await masks[0]!["type"]!.GetValue<string>().Should().BeEqualTo("mkcp-legacy");
+        await (masks[0]!["settings"]?["value"]?.GetValue<string>()).Should().BeEqualTo(seed);
+        await (masks[0]!["settings"]?["header"]?.GetValue<string>()).Should().BeNull();
+        if (expectedCount == 2)
+        {
+            await masks[1]!["type"]!.GetValue<string>().Should().BeEqualTo("mkcp-legacy");
+            await masks[1]!["settings"]!["header"]!.GetValue<string>().Should().BeEqualTo(header);
+        }
+    }
+
     [Test]
     [Arguments(null)]
     [Arguments("")]
diff --git a/v2rayN/ServiceLib/Services/CoreConfig/V2ray/V2rayOutboundService.cs b/v2rayN/ServiceLib/Services/CoreConfig/V2ray/V2rayOutboundService.cs
index 9e252c0a..47f9ce0c 100644
--- a/v2rayN/ServiceLib/Services/CoreConfig/V2ray/V2rayOutboundService.cs
+++ b/v2rayN/ServiceLib/Services/CoreConfig/V2ray/V2rayOutboundService.cs
@@ -412,14 +412,11 @@ public partial class CoreConfigV2rayService
                     }
                     if (Global.KcpHeaderMaskMap.TryGetValue(headerType, out var header))
                     {
-                        kcpFinalmask.udp =
-                        [
-                            new Mask4Ray
-                            {
-                                type = "mkcp-legacy",
-                                settings = new MaskSettings4Ray { header = header },
-                            },
-                        ];
+                        kcpFinalmask.udp.Add(new Mask4Ray
+                        {
+                            type = "mkcp-legacy",
+                            settings = new MaskSettings4Ray { header = header },
+                        });
                     }
                     streamSettings.kcpSettings = kcpSettings;
                     streamSettings.finalmask = (JsonObject)JsonUtils.SerializeToNode(kcpFinalmask);