diff --git a/TBF/Rig/RegisterReaders/PoseidonCmdStartStop/CliRunner.cs b/TBF/Rig/RegisterReaders/PoseidonCmdStartStop/CliRunner.cs
index 6511300e9..146868d93 100644
--- a/TBF/Rig/RegisterReaders/PoseidonCmdStartStop/CliRunner.cs
+++ b/TBF/Rig/RegisterReaders/PoseidonCmdStartStop/CliRunner.cs
@@ -267,7 +267,7 @@ namespace TBF.Rig.RegisterReaders.PoseidonCmdStartStop
 
                     if (info.ExitCode != 0)
                     {
-                        info.FailureReason = $"CLI exited with code {info.ExitCode}.";
+                        info.FailureReason = $"CLI exited with exit code {info.ExitCode}.";
                         log?.Error($"{info.Name}: {info.FailureReason} stderr='{info.StandardError}'");
                     }
 
@@ -300,8 +300,10 @@ namespace TBF.Rig.RegisterReaders.PoseidonCmdStartStop
 
         public void AddRunAndCaptureJsonAsync<T>(string fileName, string args) where T : new()
         {
-            log.Debug($"CLI: {fileName}");
-            log.Debug($"ARGS: {args}");
+            // Tests deliberately create CliRunner without a logger. Starting a CLI task
+            // must not depend on diagnostics being configured.
+            log?.Debug($"CLI: {fileName}");
+            log?.Debug($"ARGS: {args}");
             
             ResetStartTime();
 
@@ -338,10 +340,10 @@ namespace TBF.Rig.RegisterReaders.PoseidonCmdStartStop
                 try
                 {
                     
-                    log.Debug($"FileName = '{psi.FileName}'");
-                    log.Debug($"Arguments = '{psi.Arguments}'");
-                    log.Debug($"WorkingDirectory = '{psi.WorkingDirectory}'");
-                    log.Debug($"Exists = {System.IO.File.Exists(psi.FileName)}");
+                    log?.Debug($"FileName = '{psi.FileName}'");
+                    log?.Debug($"Arguments = '{psi.Arguments}'");
+                    log?.Debug($"WorkingDirectory = '{psi.WorkingDirectory}'");
+                    log?.Debug($"Exists = {System.IO.File.Exists(psi.FileName)}");
                     
                     process.Start();
 
@@ -375,7 +377,7 @@ namespace TBF.Rig.RegisterReaders.PoseidonCmdStartStop
 
                     if (info.ExitCode != 0)
                     {
-                        info.FailureReason = $"CLI exited with code {info.ExitCode}.";
+                        info.FailureReason = $"CLI exited with exit code {info.ExitCode}.";
                         log?.Error($"{info.Name}: {info.FailureReason} stderr='{info.StandardError}'");
                         info.State = CliTaskState.Completed;
                         return default(T);
diff --git a/TBFTests/Rig/RegisterReaders/PoseidonCmdStartStop/CliRunnerTimeoutTest.cs b/TBFTests/Rig/RegisterReaders/PoseidonCmdStartStop/CliRunnerTimeoutTest.cs
index 4d312fb37..e0cc11508 100644
--- a/TBFTests/Rig/RegisterReaders/PoseidonCmdStartStop/CliRunnerTimeoutTest.cs
+++ b/TBFTests/Rig/RegisterReaders/PoseidonCmdStartStop/CliRunnerTimeoutTest.cs
@@ -45,7 +45,7 @@ namespace TBFTests.Rig.RegisterReaders.PoseidonCmdStartStop
             string args = serialPort.DefaultArgSettings(SerialPortData.EMeterArg.AllParams);
 
             Assert.AreEqual(
-                "-p COM3 -m Poseidon --hat mth --timeout 30 --operation readall",
+                "-p COM3 -m 74 --hat mth --timeout 30 --operation readall",
                 args);
         }