diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerArrayTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerArrayTests.cs
index fb03a669..2dfce4d1 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerArrayTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer.Tests/NodeManagerArrayTests.cs
@@ -43,6 +43,26 @@ public sealed class NodeManagerArrayTests : IDisposable
         await host.DisposeAsync();
     }
 
+    /// <summary>When arrayLength is null the created node must still be a 1-D array (ValueRank=OneDimension)
+    /// with ArrayDimensions [0] — the "unfixed-length" contract.</summary>
+    [Fact]
+    public async Task EnsureVariable_with_null_arrayLength_sets_dimension_zero()
+    {
+        var (host, server) = await BootAsync();
+        var nm = server.NodeManager!;
+
+        nm.EnsureVariable("eq-1/arr-unfixed", parentFolderNodeId: null, displayName: "arr-unfixed", dataType: "Int32",
+            writable: false, historianTagname: null, isArray: true, arrayLength: null);
+
+        var variable = nm.TryGetVariable("eq-1/arr-unfixed");
+        variable.ShouldNotBeNull();
+        variable!.ValueRank.ShouldBe(ValueRanks.OneDimension);
+        variable.ArrayDimensions.ShouldNotBeNull();
+        variable.ArrayDimensions.ShouldBe(new uint[] { 0u });
+
+        await host.DisposeAsync();
+    }
+
     /// <summary>A default (scalar) EnsureVariable call keeps ValueRank=Scalar and leaves
     /// ArrayDimensions null/empty.</summary>
     [Fact]
@@ -57,7 +77,7 @@ public sealed class NodeManagerArrayTests : IDisposable
         var variable = nm.TryGetVariable("eq-1/scalar");
         variable.ShouldNotBeNull();
         variable!.ValueRank.ShouldBe(ValueRanks.Scalar);
-        (variable.ArrayDimensions is null || variable.ArrayDimensions.Count == 0).ShouldBeTrue();
+        variable.ArrayDimensions.ShouldBeNull();
 
         await host.DisposeAsync();
     }