diff --git a/src/Tools/dotnet-stack/ReportCommand.cs b/src/Tools/dotnet-stack/ReportCommand.cs
index 324c299532..76ca818ead 100644
--- a/src/Tools/dotnet-stack/ReportCommand.cs
+++ b/src/Tools/dotnet-stack/ReportCommand.cs
@@ -121,7 +121,11 @@ private static async Task<int> Report(CancellationToken ct, IConsole console, in
                         // Thread id is in the frame name as "Thread (<ID>)"
                         string template = "Thread (";
                         string threadFrame = stackSource.GetFrameName(stackSource.GetFrameIndex(stackIndex), false);
-                        int threadId = int.Parse(threadFrame.Substring(template.Length, threadFrame.Length - (template.Length + 1)));
+
+                        // we are looking for the first index of ) because
+                        // we need to handle a thread name like: Thread (4008) (.NET IO ThreadPool Worker)
+                        int firstIndex = threadFrame.IndexOf(')');
+                        int threadId = int.Parse(threadFrame.AsSpan(template.Length, firstIndex - template.Length));
 
                         if (samplesForThread.TryGetValue(threadId, out List<StackSourceSample> samples))
                         {