diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipTransportSwitchTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipTransportSwitchTests.cs
index a657b891..0b274df2 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipTransportSwitchTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.AbCip.Tests/AbCipTransportSwitchTests.cs
@@ -116,7 +116,7 @@ public sealed class AbCipTransportSwitchTests
         native.Ok.ShouldBeFalse();
         native.Message.ShouldNotBeNull();
         native.Message!.ShouldContain("CIP handshake failed: Connection lost");
-        lib.Message.ShouldNotContain("Connection lost");
+        lib.Message!.ShouldNotContain("Connection lost");
     }
 
     /// <summary>The probe deserialises with its own string-enum converter; a bad transport is a config error.</summary>