diff --git a/tests/BenchmarkDotNet.Tests/Validators/ExecutionValidatorTests.cs b/tests/BenchmarkDotNet.Tests/Validators/ExecutionValidatorTests.cs
index 4fc70a9fb2..88267a5181 100644
--- a/tests/BenchmarkDotNet.Tests/Validators/ExecutionValidatorTests.cs
+++ b/tests/BenchmarkDotNet.Tests/Validators/ExecutionValidatorTests.cs
@@ -10,6 +10,7 @@
 
 namespace BenchmarkDotNet.Tests.Validators
 {
+    [Collection("Disable parallelism due to a bug: https://github.com/xunit/xunit/issues/2587")]
     public class ExecutionValidatorTests
     {
         [Fact]
diff --git a/tests/BenchmarkDotNet.Tests/Validators/ReturnValueValidatorTests.cs b/tests/BenchmarkDotNet.Tests/Validators/ReturnValueValidatorTests.cs
index bfa07f519b..2a08587834 100644
--- a/tests/BenchmarkDotNet.Tests/Validators/ReturnValueValidatorTests.cs
+++ b/tests/BenchmarkDotNet.Tests/Validators/ReturnValueValidatorTests.cs
@@ -11,6 +11,7 @@
 
 namespace BenchmarkDotNet.Tests.Validators
 {
+    [Collection("Disable parallelism due to a bug: https://github.com/xunit/xunit/issues/2587")]
     public class ReturnValueValidatorTests
     {
         private const string ErrorMessagePrefix = "Inconsistent benchmark return values";