diff --git a/eng/Versions.props b/eng/Versions.props
index 0c5d9017d45581..c82f159232090c 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -88,6 +88,7 @@
     <StyleCopAnalyzersVersion>1.2.0-beta.304</StyleCopAnalyzersVersion>
     <SystemBuffersVersion>4.5.1</SystemBuffersVersion>
     <SystemCollectionsVersion>4.3.0</SystemCollectionsVersion>
+    <SystemCollectionsImmutableVersion>5.0.0</SystemCollectionsImmutableVersion>
     <SystemComponentModelAnnotationsVersion>5.0.0</SystemComponentModelAnnotationsVersion>
     <SystemDataSqlClientVersion>4.8.2</SystemDataSqlClientVersion>
     <SystemDataDataSetExtensionsVersion>4.5.0</SystemDataDataSetExtensionsVersion>
diff --git a/src/coreclr/tools/aot/ILCompiler.DependencyAnalysisFramework/ILCompiler.DependencyAnalysisFramework.csproj b/src/coreclr/tools/aot/ILCompiler.DependencyAnalysisFramework/ILCompiler.DependencyAnalysisFramework.csproj
index 291136d46ae916..c98ffb07608364 100644
--- a/src/coreclr/tools/aot/ILCompiler.DependencyAnalysisFramework/ILCompiler.DependencyAnalysisFramework.csproj
+++ b/src/coreclr/tools/aot/ILCompiler.DependencyAnalysisFramework/ILCompiler.DependencyAnalysisFramework.csproj
@@ -16,11 +16,8 @@
     <Configurations>Debug;Release;Checked</Configurations>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="System.Xml.ReaderWriter">
-      <Version>4.3.0</Version>
-    </PackageReference>
     <PackageReference Include="System.Collections.Immutable">
-      <Version>1.3.1</Version>
+      <Version>$(SystemCollectionsImmutableVersion)</Version>
     </PackageReference>
   </ItemGroup>
   <ItemGroup>
diff --git a/src/coreclr/tools/aot/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj b/src/coreclr/tools/aot/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj
index 82452cfa3e9c6d..86b9c06a6cf0d2 100644
--- a/src/coreclr/tools/aot/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj
+++ b/src/coreclr/tools/aot/ILCompiler.TypeSystem.ReadyToRun/ILCompiler.TypeSystem.ReadyToRun.csproj
@@ -26,9 +26,6 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="System.IO.MemoryMappedFiles">
-      <Version>4.3.0</Version>
-    </PackageReference>
     <PackageReference Include="System.Reflection.Metadata">
       <Version>$(SystemReflectionMetadataVersion)</Version>
     </PackageReference>
diff --git a/src/coreclr/tools/aot/crossgen2/Program.cs b/src/coreclr/tools/aot/crossgen2/Program.cs
index ef3eed5bb2f184..4df45e3065e0d3 100644
--- a/src/coreclr/tools/aot/crossgen2/Program.cs
+++ b/src/coreclr/tools/aot/crossgen2/Program.cs
@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System;
+using System.Buffers.Binary;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.IO;
@@ -696,13 +697,13 @@ private void RunSingleCompilation(Dictionary<string, string> inFilePaths, Instru
 
                     if (_commandLineOptions.CompositeKeyFile != null)
                     {
-                        ImmutableArray<byte> compositeStrongNameKey = File.ReadAllBytes(_commandLineOptions.CompositeKeyFile).ToImmutableArray();
+                        byte[] compositeStrongNameKey = File.ReadAllBytes(_commandLineOptions.CompositeKeyFile);
                         if (!IsValidPublicKey(compositeStrongNameKey))
                         {
                             throw new Exception(string.Format(SR.ErrorCompositeKeyFileNotPublicKey));
                         }
 
-                        compositeImageSettings.PublicKey = compositeStrongNameKey;
+                        compositeImageSettings.PublicKey = compositeStrongNameKey.ToImmutableArray();
                     }
 
                     //
@@ -954,7 +955,7 @@ public AlgorithmId(uint flags)
             }
         }
 
-        private static readonly ImmutableArray<byte> s_ecmaKey = ImmutableArray.Create(new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0 });
+        private static ReadOnlySpan<byte> s_ecmaKey => new byte[] { 0, 0, 0, 0, 0, 0, 0, 0, 4, 0, 0, 0, 0, 0, 0, 0 };
 
         private const int SnPublicKeyBlobSize = 13;
 
@@ -968,15 +969,21 @@ public AlgorithmId(uint flags)
         // From StrongNameInternal.cpp
         // Checks to see if a public key is a valid instance of a PublicKeyBlob as
         // defined in StongName.h
-        internal static bool IsValidPublicKey(ImmutableArray<byte> blob)
+        internal static bool IsValidPublicKey(byte[] blob)
         {
             // The number of public key bytes must be at least large enough for the header and one byte of data.
-            if (blob.IsDefault || blob.Length < s_publicKeyHeaderSize + 1)
+            if (blob.Length < s_publicKeyHeaderSize + 1)
             {
                 return false;
             }
 
-            var blobReader = new BinaryReader(new MemoryStream(blob.ToArray()));
+            // Check for the ECMA key, which does not obey the invariants checked below.
+            if (blob.AsSpan().SequenceEqual(s_ecmaKey))
+            {
+                return true;
+            }
+
+            var blobReader = new BinaryReader(new MemoryStream(blob, writable: false));
 
             // Signature algorithm ID
             var sigAlgId = blobReader.ReadUInt32();
@@ -993,12 +1000,6 @@ internal static bool IsValidPublicKey(ImmutableArray<byte> blob)
                 return false;
             }
 
-            // Check for the ECMA key, which does not obey the invariants checked below.
-            if (System.Linq.Enumerable.SequenceEqual(blob, s_ecmaKey))
-            {
-                return true;
-            }
-
             // The public key must be in the wincrypto PUBLICKEYBLOB format
             if (publicKey != PublicKeyBlobId)
             {