diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Model/ConfigurationRuleFollower.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Model/ConfigurationRuleFollower.cs
index 85247146..6d65615a 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Model/ConfigurationRuleFollower.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Model/ConfigurationRuleFollower.cs
@@ -6,7 +6,7 @@ namespace Microsoft.VisualStudio.SolutionPersistence.Model;
 /// <summary>
 /// Helper to process configuration rules.
 /// </summary>
-internal readonly struct ConfigurationRuleFollower(IReadOnlyList<ConfigurationRule>? configurationRules)
+internal readonly ref struct ConfigurationRuleFollower(IReadOnlyList<ConfigurationRule>? configurationRules)
 {
     private readonly IReadOnlyList<ConfigurationRule>? configurationRules = configurationRules;
 
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionConfigurationMap.Rules.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionConfigurationMap.Rules.cs
index 907de597..d374a1fd 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionConfigurationMap.Rules.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionConfigurationMap.Rules.cs
@@ -31,7 +31,7 @@ internal sealed partial class SolutionConfigurationMap
     /// </summary>
     /// <param name="projectMappings">The mappings to update.</param>
     /// <param name="scopedRules">The rules to run, scoped to their effect.</param>
-    private void ApplyRules(in SolutionToProjectMappings projectMappings, in ScopedRules scopedRules)
+    private void ApplyRules(in SolutionToProjectMappings projectMappings, scoped in ScopedRules scopedRules)
     {
         int iBuildTypeBegin = scopedRules.BuildTypeIndex == ScopedRules.All ? 0 : scopedRules.BuildTypeIndex;
         int iBuildTypeEnd = scopedRules.BuildTypeIndex == ScopedRules.All ? this.BuildTypesCount : scopedRules.BuildTypeIndex + 1;
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionConfigurationMap.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionConfigurationMap.cs
index 3a84e19e..1334316f 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionConfigurationMap.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Model/SolutionConfigurationMap.cs
@@ -9,8 +9,8 @@ namespace Microsoft.VisualStudio.SolutionPersistence.Model;
 internal sealed partial class SolutionConfigurationMap
 {
     private readonly SolutionModel solutionModel;
-    private readonly Dictionary<string, int> buildTypesIndex = [];
-    private readonly Dictionary<string, int> platformsIndex = [];
+    private readonly Dictionary<string, int> buildTypesIndex;
+    private readonly Dictionary<string, int> platformsIndex;
 
     private readonly Dictionary<SolutionProjectModel, SolutionToProjectMappings> perProjectCurrent = [];
 
@@ -19,11 +19,13 @@ internal sealed partial class SolutionConfigurationMap
     internal SolutionConfigurationMap(SolutionModel solutionModel)
     {
         this.solutionModel = solutionModel;
+        this.buildTypesIndex = new Dictionary<string, int>(solutionModel.BuildTypes.Count);
         for (int i = 0; i < solutionModel.BuildTypes.Count; i++)
         {
             this.buildTypesIndex.Add(solutionModel.BuildTypes[i], i);
         }
 
+        this.platformsIndex = new Dictionary<string, int>(solutionModel.Platforms.Count);
         for (int i = 0; i < solutionModel.Platforms.Count; i++)
         {
             this.platformsIndex.Add(PlatformNames.Canonical(solutionModel.Platforms[i]), i);
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/SlnV12/SlnV12Extensions.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/SlnV12/SlnV12Extensions.cs
index bb5b8823..055f2b5e 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/SlnV12/SlnV12Extensions.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/SlnV12/SlnV12Extensions.cs
@@ -265,8 +265,6 @@ static void SetProjectConfigurationPlatforms(SolutionModel solution, SolutionPro
                 {
                     ParseProjectConfigLine(solution, projectKey, projectValue);
                 }
-
-                solution.DistillProjectConfigurations();
             }
 
             // Applies a .SLN configuration line to the current project configuration.
diff --git a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/SlnXMLSerializer.Writer.cs b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/SlnXMLSerializer.Writer.cs
index f34ab761..1207ab8e 100644
--- a/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/SlnXMLSerializer.Writer.cs
+++ b/src/Microsoft.VisualStudio.SolutionPersistence/Serializer/Xml/SlnXMLSerializer.Writer.cs
@@ -43,6 +43,8 @@ internal static async Task SaveAsync(
                 model.RemoveObsoleteProperties();
             }
 
+            model.DistillProjectConfigurations();
+
             // If this started as an XML document, merge the changes back into the original document.
             SlnxFile root = modelExtension?.Root ?? CreateNewSlnFile(fullPath, xmlSerializerSettings, model.StringTable);
 
diff --git a/test/Microsoft.VisualStudio.SolutionPersistence.Tests/Serialization/ManipulateXmlKitchenSink.cs b/test/Microsoft.VisualStudio.SolutionPersistence.Tests/Serialization/ManipulateXmlKitchenSink.cs
index 349717c3..b3fdd143 100644
--- a/test/Microsoft.VisualStudio.SolutionPersistence.Tests/Serialization/ManipulateXmlKitchenSink.cs
+++ b/test/Microsoft.VisualStudio.SolutionPersistence.Tests/Serialization/ManipulateXmlKitchenSink.cs
@@ -41,7 +41,7 @@ static void CreateModifiedModel(SolutionModel solution)
 
             SolutionProjectModel? project = solution.FindProject(Path.Join("other", "Project4.nativeproj"));
             Assert.NotNull(project);
-            project.AddProjectConfigurationRule(new ConfigurationRule(BuildDimension.Platform, "*", "Z80", "Z80"));
+            project.AddProjectConfigurationRule(new ConfigurationRule(BuildDimension.Platform, "*", "Arm64", "Z80"));
 
             SolutionProjectModel? project3 = solution.FindProject("Project3.csproj");
             Assert.NotNull(project3);
diff --git a/test/Microsoft.VisualStudio.SolutionPersistence.Tests/SlnAssets/SlnxWhitespace/KitchenSink-AddConfigurations.slnx.xml b/test/Microsoft.VisualStudio.SolutionPersistence.Tests/SlnAssets/SlnxWhitespace/KitchenSink-AddConfigurations.slnx.xml
index d27565f4..5c6d6a3a 100644
--- a/test/Microsoft.VisualStudio.SolutionPersistence.Tests/SlnAssets/SlnxWhitespace/KitchenSink-AddConfigurations.slnx.xml
+++ b/test/Microsoft.VisualStudio.SolutionPersistence.Tests/SlnAssets/SlnxWhitespace/KitchenSink-AddConfigurations.slnx.xml
@@ -52,7 +52,7 @@
             <BuildDependency Project="Project2.nativeproj" />
             <BuildDependency Project="Project3.csproj" />
             <BuildDependency Project="Project3.nativeproj" />
-            <Platform Solution="*|Z80" Project="Z80" />
+            <Platform Solution="*|Arm64" Project="Z80" />
         </Project>
         <Project Path="other/Project5.nativeproj" />
         <Project Path="other/Project6.nativeproj" />