diff --git a/src/ZB.MOM.WW.ScadaBridge.Transport/TransportOptionsValidator.cs b/src/ZB.MOM.WW.ScadaBridge.Transport/TransportOptionsValidator.cs
index d5dd9eb5..43799b13 100644
--- a/src/ZB.MOM.WW.ScadaBridge.Transport/TransportOptionsValidator.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.Transport/TransportOptionsValidator.cs
@@ -48,6 +48,10 @@ public sealed class TransportOptionsValidator : OptionsValidatorBase<TransportOp
             $"ScadaBridge:Transport:MaxUnlockAttemptsPerSession must be positive " +
             $"(was {options.MaxUnlockAttemptsPerSession}); it caps failed passphrase attempts before a session locks.");
 
+        builder.RequireThat(options.MaxConcurrentImportSessions > 0,
+            $"ScadaBridge:Transport:MaxConcurrentImportSessions must be positive " +
+            $"(was {options.MaxConcurrentImportSessions}); a zero/negative cap rejects every import session forever.");
+
         builder.RequireThat(options.MaxUnlockAttemptsPerIpPerHour > 0,
             $"ScadaBridge:Transport:MaxUnlockAttemptsPerIpPerHour must be positive " +
             $"(was {options.MaxUnlockAttemptsPerIpPerHour}); it caps unlock attempts per IP address per hour.");
diff --git a/tests/ZB.MOM.WW.ScadaBridge.Transport.Tests/TransportOptionsValidatorTests.cs b/tests/ZB.MOM.WW.ScadaBridge.Transport.Tests/TransportOptionsValidatorTests.cs
index 1c40c78c..47a3a213 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.Transport.Tests/TransportOptionsValidatorTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.Transport.Tests/TransportOptionsValidatorTests.cs
@@ -38,6 +38,22 @@ public class TransportOptionsValidatorTests
         Assert.Contains("MaxBundleSizeMb", result.FailureMessage);
     }
 
+    [Fact]
+    public void ZeroMaxConcurrentImportSessions_IsRejected()
+    {
+        var result = Validate(new TransportOptions { MaxConcurrentImportSessions = 0 });
+        Assert.True(result.Failed);
+        Assert.Contains("MaxConcurrentImportSessions", result.FailureMessage);   // FAILS today: validates clean
+    }
+
+    [Fact]
+    public void NegativeMaxConcurrentImportSessions_IsRejected()
+    {
+        var result = Validate(new TransportOptions { MaxConcurrentImportSessions = -1 });
+        Assert.True(result.Failed);
+        Assert.Contains("MaxConcurrentImportSessions", result.FailureMessage);
+    }
+
     [Fact]
     public void ZeroPbkdf2Iterations_IsRejected()
     {