diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 2f7ce4a..f8985ea 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -38,6 +38,9 @@ jobs:
         fileName: 'Portable.Xaml.snk'
         encodedString: ${{ secrets.STRONG_NAME_KEY }}
     
+    - name: Clear package cache as a temporary workaround for actions/setup-dotnet#155
+      run: dotnet clean && dotnet nuget locals all --clear
+
     - name: Build
       run: dotnet build ${{ env.PlatformBuildParameters }} ${{ env.BuildParameters }} "/p:AssemblyOriginatorKeyFile=${{ steps.get_strong_name.outputs.filePath }}"
 
diff --git a/src/Portable.Xaml/Portable.Xaml/PrefixLookup.cs b/src/Portable.Xaml/Portable.Xaml/PrefixLookup.cs
index 6558504..74e6054 100644
--- a/src/Portable.Xaml/Portable.Xaml/PrefixLookup.cs
+++ b/src/Portable.Xaml/Portable.Xaml/PrefixLookup.cs
@@ -70,16 +70,45 @@ public string AddNamespace (string ns)
 			string prefix, s;
 			if (ns == XamlLanguage.Xaml2006Namespace)
 				prefix = "x";
-			else if (!l.Any (i => i.Prefix == String.Empty))
+			else if (!AnyHavePrefix(l, String.Empty))
 				prefix = String.Empty;
-			else if ((s = GetAcronym (ns)) != null && !l.Any (i => i.Prefix == s))
-				prefix = s;
 			else
-				prefix = sctx.GetPreferredPrefix (ns);
+			{
+				s = GetAcronym(ns) ?? sctx.GetPreferredPrefix(ns);
+				prefix = AnyHavePrefix(l, s) ? MakePrefixAddNumber(l, s) : s;
+			}
 			l.Add (new NamespaceDeclaration (ns, prefix));
 			return prefix;
 		}
 
+		string MakePrefixAddNumber(List<NamespaceDeclaration> namespaces, string prefix) 
+		{
+			var prefixLen = prefix.Length;
+
+			int max = 0;
+			for (int i = 0; i < namespaces.Count; i++)
+			{
+				var p = namespaces[i].Prefix;
+				var suffix = !p.StartsWith(prefix) ? 0 :
+						     int.TryParse(p.Substring(prefixLen), out var idx) ? idx :
+						     0;
+				max = Math.Max(suffix, max);
+			}
+
+			return prefix + (max+1);
+		}
+
+		bool AnyHavePrefix(List<NamespaceDeclaration> namespaces, string prefix)
+		{
+			for (int i = 0; i < namespaces.Count; i++)
+			{
+				var ns = namespaces[i];
+				if (ns.Prefix == prefix)
+					return true;
+			}
+			return false;
+		}
+
 		const string pre = "clr-namespace:";
 
 		string GetAcronym (string ns)
diff --git a/src/Test/System.Xaml/XamlXmlWriterTest.cs b/src/Test/System.Xaml/XamlXmlWriterTest.cs
index 99f6918..6b5a4c6 100644
--- a/src/Test/System.Xaml/XamlXmlWriterTest.cs
+++ b/src/Test/System.Xaml/XamlXmlWriterTest.cs
@@ -1,4 +1,4 @@
-//
+//
 // Copyright (C) 2010 Novell Inc. http://novell.com
 //
 // Permission is hereby granted, free of charge, to any person obtaining
@@ -27,6 +27,7 @@
 using System.Linq;
 using System.Reflection;
 using NUnit.Framework;
+using System.Xml.Serialization;
 #if PORTABLE_XAML
 using Portable.Xaml.Markup;
 using Portable.Xaml.ComponentModel;
@@ -1281,10 +1282,114 @@ public void Write_ShoudSerializeObjectInCollection()
 				Assert.AreEqual(xaml, actual);
 			}
 		}
+
+		[Test]
+		public void Write_AcronymNonDuplicate()
+		{
+			var list = new List<object>();
+			list.Add(new Acronym.Class1());
+
+			var genXaml = XamlServices.Save(list);
+
+			// match object
+			var readList = XamlServices.Parse(genXaml);
+			Assert.AreEqual(list, readList, "#1");
+
+			// check namespace
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa=""clr-namespace:Tests.Portable.Xaml.Acronym;assembly="), "#2");
+		}
+		[Test]
+		public void Write_AcronymDuplicate1()
+		{
+			var list = new List<object>();
+			list.Add(new Acronym.Class1());
+			list.Add(new Acronym1.Class1());
+
+			var genXaml = XamlServices.Save(list);
+
+			// match object
+			var readList = XamlServices.Parse(genXaml);
+			Assert.AreEqual(list, readList, "#1");
+
+			// check namespace
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa=""clr-namespace:Tests.Portable.Xaml.Acronym;assembly="), "#2");
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa1=""clr-namespace:Tests.Portable.Xaml.Acronym1;assembly="), "#3");
+		}
+
+		[Test]
+		public void Write_AcronymDuplicate2()
+		{
+			var list = new List<object>();
+			list.Add(new Acronym.Class1());
+			list.Add(new Acronym1.Class1());
+			list.Add(new Acronym2.Class1());
+
+			var genXaml = XamlServices.Save(list);
+
+			// match object
+			var readList = XamlServices.Parse(genXaml);
+			Assert.AreEqual(list, readList, "#1");
+
+			// check namespace
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa=""clr-namespace:Tests.Portable.Xaml.Acronym;assembly="), "#2");
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa1=""clr-namespace:Tests.Portable.Xaml.Acronym1;assembly="), "#3");
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa2=""clr-namespace:Tests.Portable.Xaml.Acronym2;assembly="), "#4");
+		}
+
+		[Test]
+		public void Write_AcronymDuplicate3()
+		{
+			var list = new List<object>();
+			list.Add(new Acronym.Class1());
+			list.Add(new Acronym1.Class1());
+			list.Add(new Acronym2.Class1());
+			list.Add(new Acronym3.Class1());
+
+			var genXaml = XamlServices.Save(list);
+
+			// match object
+			var readList = XamlServices.Parse(genXaml);
+			Assert.AreEqual(list, readList, "#1");
+
+			// check namespace
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa=""clr-namespace:Tests.Portable.Xaml.Acronym;assembly="), "#2");
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa1=""clr-namespace:Tests.Portable.Xaml.Acronym1;assembly="), "#3");
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa2=""clr-namespace:Tests.Portable.Xaml.Acronym2;assembly="), "#4");
+			Assert.IsTrue(genXaml.Contains(@"xmlns:tpxa3=""clr-namespace:Tests.Portable.Xaml.Acronym3;assembly="), "#5");
+		}
 	}
 
 	public class TestXmlWriterClass1
 	{
 		public int Foo { get; set; }
 	}
+
+	namespace Acronym
+	{
+		public class Class1 { 
+			public override bool Equals(object obj)
+			{
+				if (obj == null)
+				{
+					return false;
+				}
+
+				return GetType() == obj.GetType();
+			}
+			
+			public override int GetHashCode() =>this.GetType().GetHashCode();
+		}
+	}
+	namespace Acronym1
+	{ 
+		public class Class1: Acronym.Class1 { }
+	}	
+	namespace Acronym2
+	{ 
+		public class Class1: Acronym.Class1 { }
+	}
+	namespace Acronym3
+	{ 
+		public class Class1: Acronym.Class1 { }
+	}
 }