diff --git a/test/CommandLineUtils.Tests/RemainingArgsPropertyConventionTests.cs b/test/CommandLineUtils.Tests/RemainingArgsPropertyConventionTests.cs
index fda30b1d..afe16c4a 100644
--- a/test/CommandLineUtils.Tests/RemainingArgsPropertyConventionTests.cs
+++ b/test/CommandLineUtils.Tests/RemainingArgsPropertyConventionTests.cs
@@ -10,6 +10,8 @@
 
 namespace McMaster.Extensions.CommandLineUtils.Tests
 {
+    // Uses shared static CommandMetadataRegistry - must not run in parallel with other registry tests
+    [Collection("MetadataRegistry")]
     public class RemainingArgsPropertyConventionTests : ConventionTestBase
     {
         public RemainingArgsPropertyConventionTests(ITestOutputHelper output) : base(output)
diff --git a/test/CommandLineUtils.Tests/SourceGeneration/CommandMetadataRegistryTests.cs b/test/CommandLineUtils.Tests/SourceGeneration/CommandMetadataRegistryTests.cs
index ecdea865..1e40f1fc 100644
--- a/test/CommandLineUtils.Tests/SourceGeneration/CommandMetadataRegistryTests.cs
+++ b/test/CommandLineUtils.Tests/SourceGeneration/CommandMetadataRegistryTests.cs
@@ -8,6 +8,8 @@
 
 namespace McMaster.Extensions.CommandLineUtils.Tests.SourceGeneration
 {
+    // Uses shared static CommandMetadataRegistry - must not run in parallel with other registry tests
+    [Collection("MetadataRegistry")]
     public class CommandMetadataRegistryTests
     {
         [Command(Name = "test1")]
diff --git a/test/CommandLineUtils.Tests/SourceGeneration/ConventionAotPathTests.cs b/test/CommandLineUtils.Tests/SourceGeneration/ConventionAotPathTests.cs
index 62b72e78..bfece719 100644
--- a/test/CommandLineUtils.Tests/SourceGeneration/ConventionAotPathTests.cs
+++ b/test/CommandLineUtils.Tests/SourceGeneration/ConventionAotPathTests.cs
@@ -14,6 +14,8 @@ namespace McMaster.Extensions.CommandLineUtils.Tests.SourceGeneration
     /// Tests for the AOT-friendly code paths in conventions.
     /// These tests exercise the generated metadata paths in conventions.
     /// </summary>
+    // Uses shared static CommandMetadataRegistry - must not run in parallel with other registry tests
+    [Collection("MetadataRegistry")]
     public class ConventionAotPathTests : IDisposable
     {
         public ConventionAotPathTests()
diff --git a/test/CommandLineUtils.Tests/SourceGeneration/MetadataProviderTests.cs b/test/CommandLineUtils.Tests/SourceGeneration/MetadataProviderTests.cs
index 2219bcee..fdfcdc46 100644
--- a/test/CommandLineUtils.Tests/SourceGeneration/MetadataProviderTests.cs
+++ b/test/CommandLineUtils.Tests/SourceGeneration/MetadataProviderTests.cs
@@ -8,6 +8,8 @@
 
 namespace McMaster.Extensions.CommandLineUtils.Tests.SourceGeneration
 {
+    // Uses shared static CommandMetadataRegistry - must not run in parallel with other registry tests
+    [Collection("MetadataRegistry")]
     public class MetadataProviderTests
     {
         [Command(Name = "test", Description = "A test command")]