diff --git a/src/Tgstation.Server.Api/ApiHeaders.cs b/src/Tgstation.Server.Api/ApiHeaders.cs
index 3758ec9b34..fd73f49f5d 100644
--- a/src/Tgstation.Server.Api/ApiHeaders.cs
+++ b/src/Tgstation.Server.Api/ApiHeaders.cs
@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
 using System.Net.Http.Headers;
+using System.Net.Mime;
 using System.Reflection;
 using System.Text;
 
@@ -16,11 +17,6 @@ namespace Tgstation.Server.Api
 	/// </summary>
 	public sealed class ApiHeaders
 	{
-		/// <summary>
-		/// TODO: Remove this when we upgrade to .NET Standard 2.1
-		/// </summary>
-		public const string ApplicationJson = "application/json";
-
 		/// <summary>
 		/// The <see cref="ApiVersion"/> header key
 		/// </summary>
@@ -146,9 +142,9 @@ namespace Tgstation.Server.Api
 			if (requestHeaders == null)
 				throw new ArgumentNullException(nameof(requestHeaders));
 
-			var jsonAccept = new Microsoft.Net.Http.Headers.MediaTypeHeaderValue(ApplicationJson);
+			var jsonAccept = new Microsoft.Net.Http.Headers.MediaTypeHeaderValue(MediaTypeNames.Application.Json);
 			if (!requestHeaders.Accept.Any(x => x.MediaType == jsonAccept.MediaType))
-				throw new InvalidOperationException(String.Format(CultureInfo.InvariantCulture, "Client does not accept {0}!", ApplicationJson));
+				throw new InvalidOperationException(String.Format(CultureInfo.InvariantCulture, "Client does not accept {0}!", MediaTypeNames.Application.Json));
 
 			if (!requestHeaders.Headers.TryGetValue(HeaderNames.UserAgent, out var userAgentValues) || userAgentValues.Count == 0)
 				throw new InvalidOperationException(String.Format(CultureInfo.InvariantCulture, "Missing {0} headers!", HeaderNames.UserAgent));
@@ -264,7 +260,7 @@ namespace Tgstation.Server.Api
 				throw new InvalidOperationException("Specified instance ID in constructor and SetRequestHeaders!");
 
 			headers.Clear();
-			headers.Accept.Add(new MediaTypeWithQualityHeaderValue(ApplicationJson));
+			headers.Accept.Add(new MediaTypeWithQualityHeaderValue(MediaTypeNames.Application.Json));
 			if (IsTokenAuthentication)
 				headers.Authorization = new AuthenticationHeaderValue(JwtAuthenticationScheme, Token);
 			else
diff --git a/src/Tgstation.Server.Client/ApiClient.cs b/src/Tgstation.Server.Client/ApiClient.cs
index cf1041fc86..0e107e91f8 100644
--- a/src/Tgstation.Server.Client/ApiClient.cs
+++ b/src/Tgstation.Server.Client/ApiClient.cs
@@ -6,6 +6,7 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Net;
 using System.Net.Http;
+using System.Net.Mime;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -157,7 +158,10 @@ namespace Tgstation.Server.Client
 			using (var request = new HttpRequestMessage(method, fullUri))
 			{
 				if (body != null)
-					request.Content = new StringContent(JsonConvert.SerializeObject(body, serializerSettings), Encoding.UTF8, ApiHeaders.ApplicationJson);
+					request.Content = new StringContent(
+						JsonConvert.SerializeObject(body, serializerSettings),
+						Encoding.UTF8,
+						MediaTypeNames.Application.Json);
 
 				var headersToUse = tokenRefresh ? tokenRefreshHeaders! : headers;
 				headersToUse.SetRequestHeaders(request.Headers, instanceId);
diff --git a/src/Tgstation.Server.Host/Controllers/ApiController.cs b/src/Tgstation.Server.Host/Controllers/ApiController.cs
index 5cd3865257..2ca7b9070f 100644
--- a/src/Tgstation.Server.Host/Controllers/ApiController.cs
+++ b/src/Tgstation.Server.Host/Controllers/ApiController.cs
@@ -6,6 +6,7 @@ using Serilog.Context;
 using System;
 using System.Linq;
 using System.Net;
+using System.Net.Mime;
 using System.Threading.Tasks;
 using Tgstation.Server.Api;
 using Tgstation.Server.Api.Models;
@@ -17,7 +18,7 @@ namespace Tgstation.Server.Host.Controllers
 	/// <summary>
 	/// A <see cref="Controller"/> for API functions
 	/// </summary>
-	[Produces(ApiHeaders.ApplicationJson)]
+	[Produces(MediaTypeNames.Application.Json)]
 	[ApiController]
 	public abstract class ApiController : Controller
 	{
diff --git a/src/Tgstation.Server.Host/Controllers/BridgeController.cs b/src/Tgstation.Server.Host/Controllers/BridgeController.cs
index 3ee3155cd8..1a0e794e9a 100644
--- a/src/Tgstation.Server.Host/Controllers/BridgeController.cs
+++ b/src/Tgstation.Server.Host/Controllers/BridgeController.cs
@@ -5,9 +5,9 @@ using Newtonsoft.Json;
 using Serilog.Context;
 using System;
 using System.Net;
+using System.Net.Mime;
 using System.Threading;
 using System.Threading.Tasks;
-using Tgstation.Server.Api;
 using Tgstation.Server.Host.Components.Interop;
 using Tgstation.Server.Host.Components.Interop.Bridge;
 
@@ -17,7 +17,7 @@ namespace Tgstation.Server.Host.Controllers
 	/// <see cref="Controller"/> for recieving DMAPI requests from DreamDaemon.
 	/// </summary>
 	[Route("Bridge")]
-	[Produces(ApiHeaders.ApplicationJson)]
+	[Produces(MediaTypeNames.Application.Json)]
 	public class BridgeController : Controller
 	{
 		/// <summary>
@@ -86,7 +86,7 @@ namespace Tgstation.Server.Host.Controllers
 
 				var responseJson = JsonConvert.SerializeObject(response, DMApiConstants.SerializerSettings);
 				logger.LogTrace("Bridge Response: {0}", responseJson);
-				return Content(responseJson, ApiHeaders.ApplicationJson);
+				return Content(responseJson, MediaTypeNames.Application.Json);
 			}
 		}
 	}
diff --git a/src/Tgstation.Server.Host/Core/SwaggerConfiguration.cs b/src/Tgstation.Server.Host/Core/SwaggerConfiguration.cs
index 218740c51b..7bd6d01449 100644
--- a/src/Tgstation.Server.Host/Core/SwaggerConfiguration.cs
+++ b/src/Tgstation.Server.Host/Core/SwaggerConfiguration.cs
@@ -7,6 +7,7 @@ using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Net;
+using System.Net.Mime;
 using Tgstation.Server.Api;
 using Tgstation.Server.Api.Models;
 using Tgstation.Server.Api.Rights;
@@ -34,7 +35,7 @@ namespace Tgstation.Server.Host.Core
 			var errorMessageContent = new Dictionary<string, OpenApiMediaType>
 			{
 				{
-					ApiHeaders.ApplicationJson,
+					MediaTypeNames.Application.Json,
 					new OpenApiMediaType
 					{
 						Schema = new OpenApiSchema
@@ -90,6 +91,12 @@ namespace Tgstation.Server.Host.Core
 				Content = errorMessageContent
 			});
 
+			AddDefaultResponse(HttpStatusCode.NotAcceptable, new OpenApiResponse
+			{
+				Description = "Invalid Accept header, TGS requires `Accept: application/json`.",
+				Content = errorMessageContent
+			});
+
 			AddDefaultResponse(HttpStatusCode.InternalServerError, new OpenApiResponse
 			{
 				Description = ErrorCode.InternalServerError.Describe(),