diff --git a/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/XmlnsCache.cs b/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/XmlnsCache.cs
index 03fe3eb9ce9..0d8d8ff9139 100644
--- a/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/XmlnsCache.cs
+++ b/src/Microsoft.DotNet.Wpf/src/PresentationFramework/System/Windows/Markup/XmlnsCache.cs
@@ -12,6 +12,7 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.Collections.Specialized;
+using System.Linq;
 using System.Reflection;
 using System.Runtime.InteropServices;
 using System.Security;
@@ -93,7 +94,7 @@ private void AddReferencedAssemblies()
             List<Assembly> interestingAssemblies = new List<Assembly>();
 
             // Load all the assemblies into a list.
-            foreach(string assemblyName in _assemblyPathTable.Keys)
+            foreach(string assemblyName in _assemblyPathTable.Keys.OfType<string>().OrderBy(s => s, StringComparer.Ordinal))
             {
                 bool hasCacheInfo = true;
                 Assembly assy;