diff --git a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowRunActivityStopTests.cs b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowRunActivityStopTests.cs
index f35910f26b..239287da1a 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowRunActivityStopTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowRunActivityStopTests.cs
@@ -10,6 +10,9 @@
 
 namespace Microsoft.Agents.AI.Workflows.UnitTests;
 
+[CollectionDefinition("ObservabilityTests", DisableParallelization = true)]
+public class NoParallelizationObservabilityTests { }
+
 /// <summary>
 /// Regression test for https://github.com/microsoft/agent-framework/issues/4155
 /// Verifies that the workflow_invoke Activity is properly stopped/disposed so it gets exported