diff --git a/clients/proto/descriptors/mxaccessgw-client-v1.protoset b/clients/proto/descriptors/mxaccessgw-client-v1.protoset
index bdb64fb..b42b792 100644
Binary files a/clients/proto/descriptors/mxaccessgw-client-v1.protoset and b/clients/proto/descriptors/mxaccessgw-client-v1.protoset differ
diff --git a/src/ZB.MOM.WW.MxGateway.Tests/Configuration/GatewayOptionsTests.cs b/src/ZB.MOM.WW.MxGateway.Tests/Configuration/GatewayOptionsTests.cs
index 26e80e7..5a114af 100644
--- a/src/ZB.MOM.WW.MxGateway.Tests/Configuration/GatewayOptionsTests.cs
+++ b/src/ZB.MOM.WW.MxGateway.Tests/Configuration/GatewayOptionsTests.cs
@@ -35,7 +35,8 @@ public sealed class GatewayOptionsTests
         Assert.Equal(10, options.Worker.ShutdownTimeoutSeconds);
         Assert.Equal(5, options.Worker.HeartbeatIntervalSeconds);
         Assert.Equal(15, options.Worker.HeartbeatGraceSeconds);
-        Assert.Equal(16 * 1024 * 1024, options.Worker.MaxMessageBytes);
+        // 16 MiB public gRPC cap plus the 64 KiB worker-frame envelope reserve (IPC-03 headroom).
+        Assert.Equal((16 * 1024 * 1024) + (64 * 1024), options.Worker.MaxMessageBytes);
 
         Assert.Equal(30, options.Sessions.DefaultCommandTimeoutSeconds);
         Assert.Equal(64, options.Sessions.MaxSessions);