diff --git a/test/Seq.Extensions.Logging.Tests/Seq/Extensions/Logging/EnricherTests.cs b/test/Seq.Extensions.Logging.Tests/Seq/Extensions/Logging/EnricherTests.cs
index 18e64fd..b492ed7 100644
--- a/test/Seq.Extensions.Logging.Tests/Seq/Extensions/Logging/EnricherTests.cs
+++ b/test/Seq.Extensions.Logging.Tests/Seq/Extensions/Logging/EnricherTests.cs
@@ -6,6 +6,7 @@
 
 namespace Tests.Seq.Extensions.Logging;
 
+[Collection("SelfLog")]
 public class EnricherTests
 {
     [Fact]
diff --git a/test/Seq.Extensions.Logging.Tests/Serilog/Extensions/Logging/SerilogLoggerTests.cs b/test/Seq.Extensions.Logging.Tests/Serilog/Extensions/Logging/SerilogLoggerTests.cs
index fe7ac69..f2973bc 100644
--- a/test/Seq.Extensions.Logging.Tests/Serilog/Extensions/Logging/SerilogLoggerTests.cs
+++ b/test/Seq.Extensions.Logging.Tests/Serilog/Extensions/Logging/SerilogLoggerTests.cs
@@ -13,6 +13,7 @@
 
 namespace Tests.Serilog.Extensions.Logging;
 
+[Collection("SelfLog")]
 public class SerilogLoggerTests
 {
     static SerilogLoggerTests()
diff --git a/test/Seq.Extensions.Logging.Tests/Support/SelfLogCollection.cs b/test/Seq.Extensions.Logging.Tests/Support/SelfLogCollection.cs
new file mode 100644
index 0000000..0ed12f4
--- /dev/null
+++ b/test/Seq.Extensions.Logging.Tests/Support/SelfLogCollection.cs
@@ -0,0 +1,12 @@
+using Xunit;
+
+namespace Tests.Support;
+
+/// <summary>
+/// Tests in this collection share the process-global <c>SelfLog</c> state
+/// (a single static output sink). Running them in parallel causes writes from
+/// one test to be observed by another, producing spurious failures, so the
+/// collection is serialized.
+/// </summary>
+[CollectionDefinition("SelfLog", DisableParallelization = true)]
+public class SelfLogCollection { }
\ No newline at end of file