diff --git a/src/Tgstation.Server.Host/Components/Session/SessionController.cs b/src/Tgstation.Server.Host/Components/Session/SessionController.cs
index dc55943a72..e23aac8175 100644
--- a/src/Tgstation.Server.Host/Components/Session/SessionController.cs
+++ b/src/Tgstation.Server.Host/Components/Session/SessionController.cs
@@ -107,21 +107,6 @@ namespace Tgstation.Server.Host.Components.Session
 		/// </summary>
 		public ReattachInformation ReattachInformation { get; }
 
-		/// <summary>
-		/// The <see cref="TaskCompletionSource"/> that completes when DD makes it's first bridge request.
-		/// </summary>
-		readonly TaskCompletionSource initialBridgeRequestTcs;
-
-		/// <summary>
-		/// The <see cref="Instance"/> metadata.
-		/// </summary>
-		readonly Api.Models.Instance metadata;
-
-		/// <summary>
-		/// A <see cref="CancellationTokenSource"/> used for the topic send operation made on reattaching.
-		/// </summary>
-		readonly CancellationTokenSource reattachTopicCts;
-
 		/// <summary>
 		/// The <see cref="global::Byond.TopicSender.ITopicClient"/> for the <see cref="SessionController"/>.
 		/// </summary>
@@ -157,6 +142,26 @@ namespace Tgstation.Server.Host.Components.Session
 		/// </summary>
 		readonly IAsyncDelayer asyncDelayer;
 
+		/// <summary>
+		/// The <see cref="TaskCompletionSource"/> that completes when DD makes it's first bridge request.
+		/// </summary>
+		readonly TaskCompletionSource initialBridgeRequestTcs;
+
+		/// <summary>
+		/// The <see cref="FifoSemaphore"/> used to prevent concurrent calls into /world/Topic().
+		/// </summary>
+		readonly FifoSemaphore topicSendSemaphore;
+
+		/// <summary>
+		/// The <see cref="Instance"/> metadata.
+		/// </summary>
+		readonly Api.Models.Instance metadata;
+
+		/// <summary>
+		/// A <see cref="CancellationTokenSource"/> used for the topic send operation made on reattaching.
+		/// </summary>
+		readonly CancellationTokenSource reattachTopicCts;
+
 		/// <summary>
 		/// <see langword="lock"/> <see cref="object"/> for port updates and <see cref="disposed"/>.
 		/// </summary>
@@ -282,6 +287,8 @@ namespace Tgstation.Server.Host.Components.Session
 			// Worth further investigation as to if that sequence of events is a reliable crash vector and opening a BYOND bug if it is
 			initialBridgeRequestTcs = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
 			reattachTopicCts = new CancellationTokenSource();
+
+			topicSendSemaphore = new FifoSemaphore();
 			synchronizationLock = new object();
 
 			if (apiValidate || DMApiAvailable)
@@ -329,6 +336,11 @@ namespace Tgstation.Server.Host.Components.Session
 			}
 
 			Logger.LogTrace("Disposing...");
+
+			// yield then acquire the topic semaphore to prevent new calls from starting
+			await Task.Yield();
+			(await topicSendSemaphore.Lock(CancellationToken.None)).Dispose(); // DCT: None available
+
 			if (!released)
 			{
 				process.Terminate();
@@ -345,6 +357,8 @@ namespace Tgstation.Server.Host.Components.Session
 
 			if (!released)
 				await Lifetime; // finish the async callback
+
+			topicSendSemaphore.Dispose();
 		}
 
 		/// <inheritdoc />
@@ -387,7 +401,7 @@ namespace Tgstation.Server.Host.Components.Session
 		{
 			ArgumentNullException.ThrowIfNull(parameters);
 
-			if (Lifetime.IsCompleted)
+			if (Lifetime.IsCompleted || disposed)
 			{
 				Logger.LogWarning(
 					"Attempted to send a command to an inactive SessionController: {commandType}",
@@ -960,35 +974,45 @@ namespace Tgstation.Server.Host.Components.Session
 		/// <returns>A <see cref="Task{TResult}"/> resulting in the <see cref="CombinedTopicResponse"/> of the topic request.</returns>
 		async Task<CombinedTopicResponse> SendRawTopic(string queryString, bool priority, CancellationToken cancellationToken)
 		{
+			if (disposed)
+			{
+				Logger.LogWarning(
+					"Attempted to send a topic on a disposed SessionController");
+				return null;
+			}
+
 			var targetPort = ReattachInformation.Port;
 			var killedOrRebootedTask = Task.WhenAny(Lifetime, OnReboot);
 			global::Byond.TopicSender.TopicResponse byondResponse = null;
 			var firstSend = true;
 
-			const int PrioritySendAttempts = 5;
-			var endpoint = new IPEndPoint(IPAddress.Loopback, targetPort);
-			for (var i = PrioritySendAttempts - 1; i >= 0 && (priority || firstSend); --i)
-				try
-				{
-					firstSend = false;
-					if (!killedOrRebootedTask.IsCompleted)
-						byondResponse = await byondTopicSender.SendTopic(
-							endpoint,
-							queryString,
-							cancellationToken);
-
-					break;
-				}
-				catch (Exception ex) when (!cancellationToken.IsCancellationRequested)
-				{
-					Logger.LogWarning(ex, "SendTopic exception!{retryDetails}", priority ? $" {i} attempts remaining." : String.Empty);
-
-					if (priority && i > 0)
+			using (await topicSendSemaphore.Lock(cancellationToken))
+			{
+				const int PrioritySendAttempts = 5;
+				var endpoint = new IPEndPoint(IPAddress.Loopback, targetPort);
+				for (var i = PrioritySendAttempts - 1; i >= 0 && (priority || firstSend); --i)
+					try
 					{
-						var delayTask = asyncDelayer.Delay(TimeSpan.FromSeconds(2), cancellationToken);
-						await Task.WhenAny(killedOrRebootedTask, delayTask);
+						firstSend = false;
+						if (!killedOrRebootedTask.IsCompleted)
+							byondResponse = await byondTopicSender.SendTopic(
+								endpoint,
+								queryString,
+								cancellationToken);
+
+						break;
 					}
-				}
+					catch (Exception ex) when (!cancellationToken.IsCancellationRequested)
+					{
+						Logger.LogWarning(ex, "SendTopic exception!{retryDetails}", priority ? $" {i} attempts remaining." : String.Empty);
+
+						if (priority && i > 0)
+						{
+							var delayTask = asyncDelayer.Delay(TimeSpan.FromSeconds(2), cancellationToken);
+							await Task.WhenAny(killedOrRebootedTask, delayTask);
+						}
+					}
+			}
 
 			if (byondResponse == null)
 			{