diff --git a/src/Microsoft.AspNetCore.Hosting/Internal/HostingEnvironmentExtensions.cs b/src/Microsoft.AspNetCore.Hosting/Internal/HostingEnvironmentExtensions.cs
index b38f997cac..50be22800b 100644
--- a/src/Microsoft.AspNetCore.Hosting/Internal/HostingEnvironmentExtensions.cs
+++ b/src/Microsoft.AspNetCore.Hosting/Internal/HostingEnvironmentExtensions.cs
@@ -63,7 +63,6 @@ namespace Microsoft.AspNetCore.Hosting.Internal
             
             hostingEnvironment.EnvironmentName =
                 options.Environment ??
-                Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT") ??
                 hostingEnvironment.EnvironmentName;
         }
     }
diff --git a/src/Microsoft.AspNetCore.Hosting/WebHostBuilder.cs b/src/Microsoft.AspNetCore.Hosting/WebHostBuilder.cs
index a58f96f3ac..fae25a30ed 100644
--- a/src/Microsoft.AspNetCore.Hosting/WebHostBuilder.cs
+++ b/src/Microsoft.AspNetCore.Hosting/WebHostBuilder.cs
@@ -40,6 +40,21 @@ namespace Microsoft.AspNetCore.Hosting
             _hostingEnvironment = new HostingEnvironment();
             _configureServicesDelegates = new List<Action<IServiceCollection>>();
             _configureLoggingDelegates = new List<Action<ILoggerFactory>>();
+
+            // This may end up storing null, but that's indistinguishable from not adding it.
+            UseSetting(WebHostDefaults.EnvironmentKey, Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT")
+                // Legacy keys, never remove these.
+                ?? Environment.GetEnvironmentVariable("Hosting:Environment")
+                ?? Environment.GetEnvironmentVariable("ASPNET_ENV"));
+
+            if (Environment.GetEnvironmentVariable("Hosting:Environment") != null)
+            {
+                Console.WriteLine("The environment variable 'Hosting:Environment' is obsolete and has been replaced with 'ASPNETCORE_ENVIRONMENT'");
+            }
+            if (Environment.GetEnvironmentVariable("ASPNET_ENV") != null)
+            {
+                Console.WriteLine("The environment variable 'ASPNET_ENV' is obsolete and has been replaced with 'ASPNETCORE_ENVIRONMENT'");
+            }
         }
 
         /// <summary>