diff --git a/src/Microsoft.AspNetCore.SystemWebAdapters/Adapters/ProxyHeaderModule.Framework.cs b/src/Microsoft.AspNetCore.SystemWebAdapters/Adapters/ProxyHeaderModule.Framework.cs
index 8031f1f00c..77bd7a742a 100644
--- a/src/Microsoft.AspNetCore.SystemWebAdapters/Adapters/ProxyHeaderModule.Framework.cs
+++ b/src/Microsoft.AspNetCore.SystemWebAdapters/Adapters/ProxyHeaderModule.Framework.cs
@@ -20,8 +20,10 @@ internal class ProxyHeaderModule : IHttpModule
     private const string ServerPort = "SERVER_PORT";
     private const string ForwardedProto = "x-forwarded-proto";
     private const string ForwardedHost = "x-forwarded-host";
-    private const string On = "ON";
-    private const string Off = "OFF";
+    
+    // ASP.NET expects lowercase values for HTTPS, not uppercase as the docs may indicate
+    private const string On = "on";
+    private const string Off = "off";
 
     private readonly IOptions<ProxyOptions> _options;
 
diff --git a/test/Microsoft.AspNetCore.SystemWebAdapters.Framework.Tests/ProxyHeaderModuleTests.cs b/test/Microsoft.AspNetCore.SystemWebAdapters.Framework.Tests/ProxyHeaderModuleTests.cs
index b454b472fb..3a68ba62e8 100644
--- a/test/Microsoft.AspNetCore.SystemWebAdapters.Framework.Tests/ProxyHeaderModuleTests.cs
+++ b/test/Microsoft.AspNetCore.SystemWebAdapters.Framework.Tests/ProxyHeaderModuleTests.cs
@@ -18,8 +18,8 @@ public class ProxyHeaderModuleTests
     private const string ServerName = "SERVER_NAME";
     private const string ServerPort = "SERVER_PORT";
     private const string ServerHttps = "HTTPS";
-    private const string On = "ON";
-    private const string Off = "OFF";
+    private const string On = "on";
+    private const string Off = "off";
 
     [Fact]
     public void NoHeaderChange()