diff --git a/source/Halibut.Tests/BadCertificatesTests.cs b/source/Halibut.Tests/BadCertificatesTests.cs
index ee65c2da..00ee8e3a 100644
--- a/source/Halibut.Tests/BadCertificatesTests.cs
+++ b/source/Halibut.Tests/BadCertificatesTests.cs
@@ -18,6 +18,7 @@
 
 namespace Halibut.Tests
 {
+    [NonParallelizable]
     public class BadCertificatesTests : BaseTest
     {
         [Test]
diff --git a/source/Halibut.Tests/CancellationViaClientProxyFixture.cs b/source/Halibut.Tests/CancellationViaClientProxyFixture.cs
index df52164b..b8936eda 100644
--- a/source/Halibut.Tests/CancellationViaClientProxyFixture.cs
+++ b/source/Halibut.Tests/CancellationViaClientProxyFixture.cs
@@ -17,6 +17,7 @@
 
 namespace Halibut.Tests
 {
+    [NonParallelizable]
     public class CancellationViaClientProxyFixture : BaseTest
     {
         [Test]
diff --git a/source/Halibut.Tests/ProxyFixture.cs b/source/Halibut.Tests/ProxyFixture.cs
index 907057d9..c7029fc8 100644
--- a/source/Halibut.Tests/ProxyFixture.cs
+++ b/source/Halibut.Tests/ProxyFixture.cs
@@ -11,6 +11,7 @@
 
 namespace Halibut.Tests
 {
+    [NonParallelizable]
     public class ProxyFixture : BaseTest
     {
         [Test]