diff --git a/tests/FSharp.Compiler.Service.Tests/PerfTests.fs b/tests/FSharp.Compiler.Service.Tests/PerfTests.fs
index 0a58bd4ec72..8a417cec07c 100644
--- a/tests/FSharp.Compiler.Service.Tests/PerfTests.fs
+++ b/tests/FSharp.Compiler.Service.Tests/PerfTests.fs
@@ -1,4 +1,6 @@
-module FSharp.Compiler.Service.Tests.PerfTests
+// Because of global static FSharpChecker.ActualCheckFileCount
+[<Xunit.Collection(nameof FSharp.Test.DoNotRunInParallel)>]
+module FSharp.Compiler.Service.Tests.PerfTests
 
 open Xunit
 open FsUnit