diff --git a/src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo.cs b/src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo.cs
index 7cd92e10fc344ae1ba31af925a4ddf19d9c68114..da945b4bc2771e5b71a5cd366281d09d4564c585 100644
--- a/src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo.cs
+++ b/src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo.cs
@@ -7,6 +7,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Roslyn.Utilities;
+using static Roslyn.Utilities.PortableShim;
 
 namespace Microsoft.CodeAnalysis.FindSymbols
 {
@@ -236,7 +237,6 @@ internal static SymbolTreeInfo Create(VersionStamp version, IAssemblySymbol asse
             GenerateNodes(assembly.GlobalNamespace, list);
 
             var spellChecker = new SpellChecker(list.Select(n => n.Name));
-
             return new SymbolTreeInfo(version, SortNodes(list), spellChecker);
         }
 
diff --git a/src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo_Serialization.cs b/src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo_Serialization.cs
index 102608a1c9a5457696bc7e6c254eb9f14ee4eac9..03c8c9bae1157cd0f0a4f9793b886b910dbf4db7 100644
--- a/src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo_Serialization.cs
+++ b/src/Workspaces/Core/Portable/FindSymbols/SymbolTree/SymbolTreeInfo_Serialization.cs
@@ -13,7 +13,7 @@ namespace Microsoft.CodeAnalysis.FindSymbols
     internal partial class SymbolTreeInfo : IObjectWritable
     {
         private const string PrefixMetadataSymbolTreeInfo = "<MetadataSymbolTreeInfoPersistence>_";
-        private const string SerializationFormat = "8";
+        private const string SerializationFormat = "9";
 
         /// <summary>
         /// this is for a metadata reference in a solution
diff --git a/src/Workspaces/Core/Portable/Utilities/BKTree.Builder.cs b/src/Workspaces/Core/Portable/Utilities/BKTree.Builder.cs
index 1f63071b141d11fe9c044849996182cc1632e144..03b4be9d97f7b2ccb02902acff0a8364085fc9ba 100644
--- a/src/Workspaces/Core/Portable/Utilities/BKTree.Builder.cs
+++ b/src/Workspaces/Core/Portable/Utilities/BKTree.Builder.cs
@@ -105,7 +105,7 @@ public Builder(IEnumerable<string> values)
 
                     foreach (var ch in value)
                     {
-                        _concatenatedLowerCaseWords[characterIndex] = char.ToLower(ch);
+                        _concatenatedLowerCaseWords[characterIndex] = CaseInsensitiveComparison.ToLower(ch);
                         characterIndex++;
                     }
                 }
diff --git a/src/Workspaces/Core/Portable/Utilities/BKTree.cs b/src/Workspaces/Core/Portable/Utilities/BKTree.cs
index 273d41588fdc5a591d4a3b22a0b2b767f828570f..465ccfd2f9619172a6af07589aeb302bf8e3a8aa 100644
--- a/src/Workspaces/Core/Portable/Utilities/BKTree.cs
+++ b/src/Workspaces/Core/Portable/Utilities/BKTree.cs
@@ -4,6 +4,7 @@
 using System.Collections.Immutable;
 using System.Linq;
 using System.Text;
+using Microsoft.CodeAnalysis;
 using Roslyn.Utilities;
 using static System.Math;
 
@@ -82,7 +83,7 @@ public IList<string> Find(string value, int? threshold = null)
             {
                 for (var i = 0; i < value.Length; i++)
                 {
-                    lowerCaseCharacters[i] = char.ToLower(value[i]);
+                    lowerCaseCharacters[i] = CaseInsensitiveComparison.ToLower(value[i]);
                 }
 
                 threshold = threshold ?? WordSimilarityChecker.GetThreshold(value);
diff --git a/src/Workspaces/Core/Portable/Utilities/EditDistance.cs b/src/Workspaces/Core/Portable/Utilities/EditDistance.cs
index 83ba513765cb718dc337d47ff08c3efe911ae906..432ac30da1fc6e84bf8a576520d4bf29d2c5aa16 100644
--- a/src/Workspaces/Core/Portable/Utilities/EditDistance.cs
+++ b/src/Workspaces/Core/Portable/Utilities/EditDistance.cs
@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Text;
+using Microsoft.CodeAnalysis;
 using static System.Math;
 
 namespace Roslyn.Utilities
@@ -61,7 +62,7 @@ private static char[] ConvertToLowercaseArray(string text)
             var array = ArrayPool<char>.GetArray(text.Length);
             for (int i = 0; i < text.Length; i++)
             {
-                array[i] = char.ToLower(text[i]);
+                array[i] = CaseInsensitiveComparison.ToLower(text[i]);
             }
 
             return array;