diff --git a/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.cs b/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.cs
index 9a73882b9e3a7..e23fd718f00d7 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.cs
@@ -8,8 +8,8 @@ namespace Microsoft.Extensions.Configuration
 {
     public static partial class IniConfigurationExtensions
     {
-        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddIniFile(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, Microsoft.Extensions.FileProviders.IFileProvider provider, string path, bool optional, bool reloadOnChange) { throw null; }
-        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddIniFile(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, System.Action<Microsoft.Extensions.Configuration.Ini.IniConfigurationSource> configureSource) { throw null; }
+        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddIniFile(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, Microsoft.Extensions.FileProviders.IFileProvider? provider, string path, bool optional, bool reloadOnChange) { throw null; }
+        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddIniFile(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, System.Action<Microsoft.Extensions.Configuration.Ini.IniConfigurationSource>? configureSource) { throw null; }
         public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddIniFile(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, string path) { throw null; }
         public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddIniFile(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, string path, bool optional) { throw null; }
         public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddIniFile(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, string path, bool optional, bool reloadOnChange) { throw null; }
@@ -32,7 +32,7 @@ public partial class IniStreamConfigurationProvider : Microsoft.Extensions.Confi
     {
         public IniStreamConfigurationProvider(Microsoft.Extensions.Configuration.Ini.IniStreamConfigurationSource source) : base (default(Microsoft.Extensions.Configuration.StreamConfigurationSource)) { }
         public override void Load(System.IO.Stream stream) { }
-        public static System.Collections.Generic.IDictionary<string, string> Read(System.IO.Stream stream) { throw null; }
+        public static System.Collections.Generic.IDictionary<string, string?> Read(System.IO.Stream stream) { throw null; }
     }
     public partial class IniStreamConfigurationSource : Microsoft.Extensions.Configuration.StreamConfigurationSource
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.csproj b/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.csproj
index 7d73ff499998a..a4ee6a2df9438 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Ini/ref/Microsoft.Extensions.Configuration.Ini.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   
   <ItemGroup>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Ini/src/IniConfigurationExtensions.cs b/src/libraries/Microsoft.Extensions.Configuration.Ini/src/IniConfigurationExtensions.cs
index 259417495a1d1..ab5442a919575 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Ini/src/IniConfigurationExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Ini/src/IniConfigurationExtensions.cs
@@ -62,7 +62,7 @@ public static IConfigurationBuilder AddIniFile(this IConfigurationBuilder builde
         /// <param name="optional">Whether the file is optional.</param>
         /// <param name="reloadOnChange">Whether the configuration should be reloaded if the file changes.</param>
         /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
-        public static IConfigurationBuilder AddIniFile(this IConfigurationBuilder builder, IFileProvider provider, string path, bool optional, bool reloadOnChange)
+        public static IConfigurationBuilder AddIniFile(this IConfigurationBuilder builder, IFileProvider? provider, string path, bool optional, bool reloadOnChange)
         {
             if (builder == null)
             {
@@ -89,7 +89,7 @@ public static IConfigurationBuilder AddIniFile(this IConfigurationBuilder builde
         /// <param name="builder">The <see cref="IConfigurationBuilder"/> to add to.</param>
         /// <param name="configureSource">Configures the source.</param>
         /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
-        public static IConfigurationBuilder AddIniFile(this IConfigurationBuilder builder, Action<IniConfigurationSource> configureSource)
+        public static IConfigurationBuilder AddIniFile(this IConfigurationBuilder builder, Action<IniConfigurationSource>? configureSource)
             => builder.Add(configureSource);
 
         /// <summary>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Ini/src/IniStreamConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration.Ini/src/IniStreamConfigurationProvider.cs
index ac71fc18f8507..9b010dc476267 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Ini/src/IniStreamConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Ini/src/IniStreamConfigurationProvider.cs
@@ -23,16 +23,16 @@ public IniStreamConfigurationProvider(IniStreamConfigurationSource source) : bas
         /// </summary>
         /// <param name="stream">The stream of INI data.</param>
         /// <returns>The <see cref="IDictionary{String, String}"/> which was read from the stream.</returns>
-        public static IDictionary<string, string> Read(Stream stream)
+        public static IDictionary<string, string?> Read(Stream stream)
         {
-            var data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+            var data = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
             using (var reader = new StreamReader(stream))
             {
                 string sectionPrefix = string.Empty;
 
                 while (reader.Peek() != -1)
                 {
-                    string rawLine = reader.ReadLine();
+                    string rawLine = reader.ReadLine()!; // Since Peak didn't return -1, stream hasn't ended.
                     string line = rawLine.Trim();
 
                     // Ignore blank lines
@@ -41,7 +41,7 @@ public static IDictionary<string, string> Read(Stream stream)
                         continue;
                     }
                     // Ignore comments
-                    if (line[0] == ';' || line[0] == '#' || line[0] == '/')
+                    if (line[0] is ';' or '#' or '/')
                     {
                         continue;
                     }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Ini/src/Microsoft.Extensions.Configuration.Ini.csproj b/src/libraries/Microsoft.Extensions.Configuration.Ini/src/Microsoft.Extensions.Configuration.Ini.csproj
index 7b0a14abec59c..a212999573c80 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Ini/src/Microsoft.Extensions.Configuration.Ini.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Ini/src/Microsoft.Extensions.Configuration.Ini.csproj
@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
     <EnableDefaultItems>true</EnableDefaultItems>
     <!-- Use targeting pack references instead of granular ones in the project file. -->
     <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>