diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.cs b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.cs
index 5292b3f6d90503..6be0732e7d2f4d 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.cs
@@ -9,8 +9,8 @@ namespace Microsoft.Extensions.Configuration
     public static partial class EnvironmentVariablesExtensions
     {
         public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddEnvironmentVariables(this Microsoft.Extensions.Configuration.IConfigurationBuilder configurationBuilder) { throw null; }
-        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddEnvironmentVariables(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, System.Action<Microsoft.Extensions.Configuration.EnvironmentVariables.EnvironmentVariablesConfigurationSource> configureSource) { throw null; }
-        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddEnvironmentVariables(this Microsoft.Extensions.Configuration.IConfigurationBuilder configurationBuilder, string prefix) { throw null; }
+        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddEnvironmentVariables(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, System.Action<Microsoft.Extensions.Configuration.EnvironmentVariables.EnvironmentVariablesConfigurationSource>? configureSource) { throw null; }
+        public static Microsoft.Extensions.Configuration.IConfigurationBuilder AddEnvironmentVariables(this Microsoft.Extensions.Configuration.IConfigurationBuilder configurationBuilder, string? prefix) { throw null; }
     }
 }
 namespace Microsoft.Extensions.Configuration.EnvironmentVariables
@@ -18,14 +18,14 @@ namespace Microsoft.Extensions.Configuration.EnvironmentVariables
     public partial class EnvironmentVariablesConfigurationProvider : Microsoft.Extensions.Configuration.ConfigurationProvider
     {
         public EnvironmentVariablesConfigurationProvider() { }
-        public EnvironmentVariablesConfigurationProvider(string prefix) { }
+        public EnvironmentVariablesConfigurationProvider(string? prefix) { }
         public override void Load() { }
         public override string ToString() { throw null; }
     }
     public partial class EnvironmentVariablesConfigurationSource : Microsoft.Extensions.Configuration.IConfigurationSource
     {
         public EnvironmentVariablesConfigurationSource() { }
-        public string Prefix { get { throw null; } set { } }
+        public string? Prefix { get { throw null; } set { } }
         public Microsoft.Extensions.Configuration.IConfigurationProvider Build(Microsoft.Extensions.Configuration.IConfigurationBuilder builder) { throw null; }
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
index ac7b4214362cde..dfb3265e9954ad 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/ref/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
@@ -1,10 +1,20 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
+
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.EnvironmentVariables.cs" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\ref\Microsoft.Extensions.Configuration.csproj" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
   </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+  </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and '$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <Reference Include="System.Runtime" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesConfigurationProvider.cs
index 5ea29116ca2d9b..8b88483620cc50 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesConfigurationProvider.cs
@@ -29,7 +29,7 @@ public EnvironmentVariablesConfigurationProvider() =>
         /// Initializes a new instance with the specified prefix.
         /// </summary>
         /// <param name="prefix">A prefix used to filter the environment variables.</param>
-        public EnvironmentVariablesConfigurationProvider(string prefix) =>
+        public EnvironmentVariablesConfigurationProvider(string? prefix) =>
             _prefix = prefix ?? string.Empty;
 
         /// <summary>
@@ -47,7 +47,7 @@ public override string ToString()
 
         internal void Load(IDictionary envVariables)
         {
-            var data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+            var data = new Dictionary<string, string?>(StringComparer.OrdinalIgnoreCase);
 
             IDictionaryEnumerator e = envVariables.GetEnumerator();
             try
@@ -56,7 +56,7 @@ internal void Load(IDictionary envVariables)
                 {
                     DictionaryEntry entry = e.Entry;
                     string key = (string)entry.Key;
-                    string provider = null;
+                    string? provider = null;
                     string prefix;
 
                     if (key.StartsWith(MySqlServerPrefix, StringComparison.OrdinalIgnoreCase))
@@ -94,7 +94,7 @@ internal void Load(IDictionary envVariables)
 
                     // Add the key-value pair for connection string, and optionally provider name
                     key = NormalizeKey(key.Substring(prefix.Length));
-                    AddIfPrefixed(data, $"ConnectionStrings:{key}", (string)entry.Value);
+                    AddIfPrefixed(data, $"ConnectionStrings:{key}", (string?)entry.Value);
                     if (provider != null)
                     {
                         AddIfPrefixed(data, $"ConnectionStrings:{key}_ProviderName", provider);
@@ -109,7 +109,7 @@ internal void Load(IDictionary envVariables)
             Data = data;
         }
 
-        private void AddIfPrefixed(Dictionary<string, string> data, string key, string value)
+        private void AddIfPrefixed(Dictionary<string, string?> data, string key, string? value)
         {
             if (key.StartsWith(_prefix, StringComparison.OrdinalIgnoreCase))
             {
diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesConfigurationSource.cs b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesConfigurationSource.cs
index f5ac7b87a4a465..66e941af7f9bf1 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesConfigurationSource.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesConfigurationSource.cs
@@ -11,7 +11,7 @@ public class EnvironmentVariablesConfigurationSource : IConfigurationSource
         /// <summary>
         /// A prefix used to filter environment variables.
         /// </summary>
-        public string Prefix { get; set; }
+        public string? Prefix { get; set; }
 
         /// <summary>
         /// Builds the <see cref="EnvironmentVariablesConfigurationProvider"/> for this source.
diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesExtensions.cs b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesExtensions.cs
index b43127513186f6..a5826a82a3a4cd 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/EnvironmentVariablesExtensions.cs
@@ -31,7 +31,7 @@ public static IConfigurationBuilder AddEnvironmentVariables(this IConfigurationB
         /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
         public static IConfigurationBuilder AddEnvironmentVariables(
             this IConfigurationBuilder configurationBuilder,
-            string prefix)
+            string? prefix)
         {
             configurationBuilder.Add(new EnvironmentVariablesConfigurationSource { Prefix = prefix });
             return configurationBuilder;
@@ -43,7 +43,7 @@ public static IConfigurationBuilder AddEnvironmentVariables(
         /// <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 AddEnvironmentVariables(this IConfigurationBuilder builder, Action<EnvironmentVariablesConfigurationSource> configureSource)
+        public static IConfigurationBuilder AddEnvironmentVariables(this IConfigurationBuilder builder, Action<EnvironmentVariablesConfigurationSource>? configureSource)
             => builder.Add(configureSource);
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
index d83ecf51782ca5..a9563d05f3346c 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.EnvironmentVariables/src/Microsoft.Extensions.Configuration.EnvironmentVariables.csproj
@@ -1,8 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <TargetFrameworks>$(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>
     <PackageDescription>Environment variables configuration provider implementation for Microsoft.Extensions.Configuration.</PackageDescription>
   </PropertyGroup>
 
@@ -10,5 +13,5 @@
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration\src\Microsoft.Extensions.Configuration.csproj" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\src\Microsoft.Extensions.Configuration.Abstractions.csproj" />
   </ItemGroup>
-
+  
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
index 0ab0a2842d7181..024ad14e46f7d2 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/ref/Microsoft.Extensions.Configuration.csproj
@@ -1,15 +1,20 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);$(NetCoreAppMinimum);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
     <Nullable>enable</Nullable>
   </PropertyGroup>
+
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.cs" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Configuration.Abstractions\ref\Microsoft.Extensions.Configuration.Abstractions.csproj" />
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
-  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
-    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections\ref\System.Collections.csproj" />
+
+  <ItemGroup Condition="'$(TargetFramework)' == '$(NetCoreAppCurrent)'">
     <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
   </ItemGroup>
+
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp' and '$(TargetFramework)' != '$(NetCoreAppCurrent)'">
+    <Reference Include="System.Runtime" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj b/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
index 10fd1c6acdcb60..f114bd7c04c31b 100644
--- a/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration/src/Microsoft.Extensions.Configuration.csproj
@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <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. -->