diff --git a/samples/aspnetcore/BasicSample/BasicSample.csproj b/samples/aspnetcore/BasicSample/BasicSample.csproj
index 04cc4e18..eac9a6b3 100644
--- a/samples/aspnetcore/BasicSample/BasicSample.csproj
+++ b/samples/aspnetcore/BasicSample/BasicSample.csproj
@@ -3,6 +3,7 @@
  <PropertyGroup>
   <TargetFramework>net5.0</TargetFramework>
   <RootNamespace>Microsoft.Examples</RootNamespace>
+  <LangVersion>default</LangVersion>
  </PropertyGroup>
 
  <ItemGroup>
diff --git a/samples/aspnetcore/ByNamespaceSample/ByNamespaceSample.csproj b/samples/aspnetcore/ByNamespaceSample/ByNamespaceSample.csproj
index 04cc4e18..eac9a6b3 100644
--- a/samples/aspnetcore/ByNamespaceSample/ByNamespaceSample.csproj
+++ b/samples/aspnetcore/ByNamespaceSample/ByNamespaceSample.csproj
@@ -3,6 +3,7 @@
  <PropertyGroup>
   <TargetFramework>net5.0</TargetFramework>
   <RootNamespace>Microsoft.Examples</RootNamespace>
+  <LangVersion>default</LangVersion>
  </PropertyGroup>
 
  <ItemGroup>
diff --git a/samples/aspnetcore/ConventionsSample/ConventionsSample.csproj b/samples/aspnetcore/ConventionsSample/ConventionsSample.csproj
index 0559b984..0dc46a41 100644
--- a/samples/aspnetcore/ConventionsSample/ConventionsSample.csproj
+++ b/samples/aspnetcore/ConventionsSample/ConventionsSample.csproj
@@ -3,6 +3,7 @@
  <PropertyGroup>
   <TargetFramework>net5.0</TargetFramework>
   <RootNamespace>Microsoft.Examples</RootNamespace>
+  <LangVersion>default</LangVersion>
  </PropertyGroup>
  
  <ItemGroup>
diff --git a/samples/aspnetcore/SwaggerSample/SwaggerSample.csproj b/samples/aspnetcore/SwaggerSample/SwaggerSample.csproj
index 94390b39..34b772cc 100644
--- a/samples/aspnetcore/SwaggerSample/SwaggerSample.csproj
+++ b/samples/aspnetcore/SwaggerSample/SwaggerSample.csproj
@@ -1,9 +1,10 @@
 <Project Sdk="Microsoft.NET.Sdk.Web">
 
  <PropertyGroup>
-  <TargetFramework>net5.0</TargetFramework>
+  <TargetFramework>netcoreapp3.1</TargetFramework>
   <RootNamespace>Microsoft.Examples</RootNamespace>
   <DocumentationFile>bin\$(Configuration)\$(TargetFramework)\$(MSBuildThisFileName).xml</DocumentationFile>
+  <LangVersion>default</LangVersion>
  </PropertyGroup>
 
  <ItemGroup>
diff --git a/samples/aspnetcore/SwaggerSample/V1/Controllers/OrdersController.cs b/samples/aspnetcore/SwaggerSample/V1/Controllers/OrdersController.cs
index de861e68..cce1c6a7 100644
--- a/samples/aspnetcore/SwaggerSample/V1/Controllers/OrdersController.cs
+++ b/samples/aspnetcore/SwaggerSample/V1/Controllers/OrdersController.cs
@@ -42,5 +42,26 @@ public IActionResult Post( [FromBody] Order order )
             order.Id = 42;
             return CreatedAtAction( nameof( Get ), new { id = order.Id }, order );
         }
+
+        /// <summary>
+        /// Updates an existing order.
+        /// </summary>
+        /// <param name="order">The order to update.</param>
+        /// <returns>The created order.</returns>
+        /// <response code="204">The order was successfully updated.</response>
+        /// <response code="400">The order is invalid.</response>
+        /// <response code="404">The order does not exist.</response>
+        [MapToApiVersion( "1.0" )]
+        [HttpPatch("{id:int}")]
+        [Produces("application/json")]
+        [Consumes("application/merge-patch+json")]
+        [ProducesResponseType(204)]
+        [ProducesResponseType(400)]
+        [ProducesResponseType(404)]
+        public IActionResult Patch(int id, [FromBody] Order order)
+        {
+            order.Id = 1; // if id=1 then it is returned from V1 OrdersController.cs
+            return CreatedAtAction(nameof(Get), new { id = order.Id }, order);
+        }
     }
 }
\ No newline at end of file
diff --git a/samples/aspnetcore/SwaggerSample/V2/Controllers/OrdersController.cs b/samples/aspnetcore/SwaggerSample/V2/Controllers/OrdersController.cs
index df50e890..f43568d3 100644
--- a/samples/aspnetcore/SwaggerSample/V2/Controllers/OrdersController.cs
+++ b/samples/aspnetcore/SwaggerSample/V2/Controllers/OrdersController.cs
@@ -63,5 +63,25 @@ public IActionResult Post( [FromBody] Order order )
             order.Id = 42;
             return CreatedAtAction( nameof( Get ), new { id = order.Id }, order );
         }
+
+        /// <summary>
+        /// Updates an existing order.
+        /// </summary>
+        /// <param name="order">The order to update.</param>
+        /// <returns>The created order.</returns>
+        /// <response code="204">The order was successfully updated.</response>
+        /// <response code="400">The order is invalid.</response>
+        /// <response code="404">The order does not exist.</response>
+        [HttpPatch( "{id:int}" )]
+        [Produces( "application/json" )]
+        [Consumes( "application/merge-patch+json" )]
+        [ProducesResponseType( 204 )]
+        [ProducesResponseType( 400 )]
+        [ProducesResponseType( 404 )]
+        public IActionResult Patch( int id, [FromBody] Order order )
+        {
+            order.Id = 2; // if id=2 then it is returned from V2 OrdersController.cs
+            return CreatedAtAction( nameof( Get ), new { id = order.Id }, order );
+        }
     }
 }
\ No newline at end of file
diff --git a/src/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.csproj b/src/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.csproj
index 8f706c64..a3269e91 100644
--- a/src/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.csproj
+++ b/src/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.csproj
@@ -8,6 +8,7 @@
   <Description>ASP.NET Core MVC API explorer functionality for discovering metadata such as the list of API-versioned controllers and actions, and their URLs and allowed HTTP methods.</Description>
   <RootNamespace>Microsoft.AspNetCore.Mvc.ApiExplorer</RootNamespace>
   <PackageTags>Microsoft;AspNet;AspNetCore;Versioning;ApiExplorer</PackageTags>
+  <LangVersion>default</LangVersion>
  </PropertyGroup>
 
  <ItemGroup>
diff --git a/src/Microsoft.AspNetCore.Mvc.Versioning/Microsoft.AspNetCore.Mvc.Versioning.csproj b/src/Microsoft.AspNetCore.Mvc.Versioning/Microsoft.AspNetCore.Mvc.Versioning.csproj
index 67d4ae64..bfe295d9 100644
--- a/src/Microsoft.AspNetCore.Mvc.Versioning/Microsoft.AspNetCore.Mvc.Versioning.csproj
+++ b/src/Microsoft.AspNetCore.Mvc.Versioning/Microsoft.AspNetCore.Mvc.Versioning.csproj
@@ -8,6 +8,7 @@
   <Description>A service API versioning library for Microsoft ASP.NET Core.</Description>
   <RootNamespace>Microsoft.AspNetCore.Mvc</RootNamespace>
   <PackageTags>Microsoft;AspNet;AspNetCore;Versioning</PackageTags>
+  <LangVersion>default</LangVersion>
  </PropertyGroup>
 
  <ItemGroup>
diff --git a/test/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.Tests/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.Tests.csproj b/test/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.Tests/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.Tests.csproj
index f6838bb6..e63d8f5c 100644
--- a/test/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.Tests/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.Tests.csproj
+++ b/test/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.Tests/Microsoft.AspNetCore.Mvc.Versioning.ApiExplorer.Tests.csproj
@@ -4,6 +4,7 @@
   <TargetFrameworks>netcoreapp3.1;net5.0</TargetFrameworks>
   <RootNamespace>Microsoft.AspNetCore.Mvc.ApiExplorer</RootNamespace>
   <PreserveCompilationContext>true</PreserveCompilationContext>
+  <LangVersion>default</LangVersion>
  </PropertyGroup>
 
  <ItemGroup>
diff --git a/test/Microsoft.AspNetCore.Mvc.Versioning.Tests/Microsoft.AspNetCore.Mvc.Versioning.Tests.csproj b/test/Microsoft.AspNetCore.Mvc.Versioning.Tests/Microsoft.AspNetCore.Mvc.Versioning.Tests.csproj
index efba2320..7d3cdf33 100644
--- a/test/Microsoft.AspNetCore.Mvc.Versioning.Tests/Microsoft.AspNetCore.Mvc.Versioning.Tests.csproj
+++ b/test/Microsoft.AspNetCore.Mvc.Versioning.Tests/Microsoft.AspNetCore.Mvc.Versioning.Tests.csproj
@@ -4,6 +4,7 @@
   <TargetFrameworks>netcoreapp3.1;net5.0</TargetFrameworks>
   <RootNamespace>Microsoft.AspNetCore.Mvc</RootNamespace>
   <PreserveCompilationContext>true</PreserveCompilationContext>
+  <LangVersion>default</LangVersion>
  </PropertyGroup>
 
  <ItemGroup>