diff --git a/src/libraries/System.Net.Http/tests/FunctionalTests/DiagnosticsTests.cs b/src/libraries/System.Net.Http/tests/FunctionalTests/DiagnosticsTests.cs
index 6fe645ce6b4513..c18b4fdecb27a8 100644
--- a/src/libraries/System.Net.Http/tests/FunctionalTests/DiagnosticsTests.cs
+++ b/src/libraries/System.Net.Http/tests/FunctionalTests/DiagnosticsTests.cs
@@ -17,9 +17,9 @@
 using Microsoft.DotNet.XUnitExtensions;
 using Xunit;
 using Xunit.Abstractions;
-
 namespace System.Net.Http.Functional.Tests
 {
+    [Collection(nameof(DisableParallelization))]
     public abstract class DiagnosticsTest : DiagnosticsTestBase
     {
         private const string EnableActivityPropagationEnvironmentVariableSettingName = "DOTNET_SYSTEM_NET_HTTP_ENABLEACTIVITYPROPAGATION";