diff --git a/src/libraries/System.Diagnostics.PerformanceCounter/src/System/Diagnostics/SharedPerformanceCounter.cs b/src/libraries/System.Diagnostics.PerformanceCounter/src/System/Diagnostics/SharedPerformanceCounter.cs
index 8d9dfd334d78b..633730d6bb14d 100644
--- a/src/libraries/System.Diagnostics.PerformanceCounter/src/System/Diagnostics/SharedPerformanceCounter.cs
+++ b/src/libraries/System.Diagnostics.PerformanceCounter/src/System/Diagnostics/SharedPerformanceCounter.cs
@@ -697,7 +697,7 @@ private unsafe CategoryData GetCategoryData()
                             }
                             else
                             {
-                                Debug.Assert(counterNamesObject is string[], $"Expected string[], got '{counterNamesObject}' with kind '{categoryKey.GetValueKind("Counter Names")}'for category '{_categoryName}'");
+                                Debug.Assert(counterNamesObject is string[], $"Expected string[], got '{counterNamesObject}' of type '{counterNamesObject?.GetType()}' with kind '{categoryKey.GetValueKind("Counter Names")}' for category '{_categoryName}'");
                                 string[] counterNames = (string[])counterNamesObject;
                                 for (int i = 0; i < counterNames.Length; i++)
                                     counterNames[i] = counterNames[i].ToLowerInvariant();