diff --git a/src/BizHawk.Client.Common/Api/BizHawkExternalToolAttribute.cs b/src/BizHawk.Client.Common/Api/BizHawkExternalToolAttribute.cs
deleted file mode 100644
index 5a73324930..0000000000
--- a/src/BizHawk.Client.Common/Api/BizHawkExternalToolAttribute.cs
+++ /dev/null
@@ -1,24 +0,0 @@
-using System;
-
-namespace BizHawk.Client.Common
-{
-	/// <remarks>This class needs to be in the assembly or old tools will throw on load instead of being recognized as old.</remarks>
-	[AttributeUsage(AttributeTargets.Assembly)]
-	[Obsolete("last used in 2.4, use [ExternalTool] instead")]
-	public sealed class BizHawkExternalToolAttribute : Attribute
-	{
-		public BizHawkExternalToolAttribute(string name, string description, string iconResourceName) {}
-		public BizHawkExternalToolAttribute(string name, string description) {}
-		public BizHawkExternalToolAttribute(string name) {}
-	}
-
-	/// <inheritdoc cref="BizHawkExternalToolAttribute"/>
-	[AttributeUsage(AttributeTargets.Assembly)]
-	[Obsolete("last used in 2.4, use [ExternalToolApplicability.*] instead")]
-	public sealed class BizHawkExternalToolUsageAttribute : Attribute
-	{
-		public BizHawkExternalToolUsageAttribute(BizHawkExternalToolUsage usage, CoreSystem system, string gameHash) {}
-		public BizHawkExternalToolUsageAttribute(BizHawkExternalToolUsage usage, CoreSystem system) {}
-		public BizHawkExternalToolUsageAttribute() {}
-	}
-}
diff --git a/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs b/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
index 6151de41b5..adbbf6652d 100644
--- a/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
+++ b/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
@@ -107,15 +107,7 @@ namespace BizHawk.Client.Common
 			Name = string.IsNullOrWhiteSpace(name) ? Guid.NewGuid().ToString() : name;
 		}
 
-		public class MissingException : Exception
-		{
-			public readonly bool OldAttributeFound;
-
-			public MissingException(bool oldAttributeFound)
-			{
-				OldAttributeFound = oldAttributeFound;
-			}
-		}
+		public class MissingException : Exception {}
 	}
 
 	[AttributeUsage(AttributeTargets.Class)]
diff --git a/src/BizHawk.Client.EmuHawk/tools/ExternalToolManager.cs b/src/BizHawk.Client.EmuHawk/tools/ExternalToolManager.cs
index 1ee41b185f..bf07bd45ac 100644
--- a/src/BizHawk.Client.EmuHawk/tools/ExternalToolManager.cs
+++ b/src/BizHawk.Client.EmuHawk/tools/ExternalToolManager.cs
@@ -74,9 +74,7 @@ namespace BizHawk.Client.EmuHawk
 				var externalToolFile = Assembly.LoadFrom(fileName);
 				var entryPoint = externalToolFile.GetTypes()
 					.SingleOrDefault(t => typeof(IExternalToolForm).IsAssignableFrom(t) && t.GetCustomAttributes().OfType<ExternalToolAttribute>().Any());
-#pragma warning disable CS0618
-				if (entryPoint == null) throw new ExternalToolAttribute.MissingException(externalToolFile.GetCustomAttributes().OfType<BizHawkExternalToolAttribute>().Any());
-#pragma warning restore CS0618
+				if (entryPoint == null) throw new ExternalToolAttribute.MissingException();
 
 				var allAttrs = entryPoint.GetCustomAttributes().ToList();
 				var applicabilityAttrs = allAttrs.OfType<ExternalToolApplicabilityAttributeBase>().ToList();
@@ -128,9 +126,7 @@ namespace BizHawk.Client.EmuHawk
 				{
 					BadImageFormatException => "This assembly can't be loaded, probably because it's corrupt or targets an incompatible .NET runtime.",
 					ExternalToolApplicabilityAttributeBase.DuplicateException => "The IExternalToolForm has conflicting applicability attributes.",
-					ExternalToolAttribute.MissingException e1 => e1.OldAttributeFound
-						? "The assembly doesn't contain a class implementing IExternalToolForm and annotated with [ExternalTool].\nHowever, the assembly itself is annotated with [BizHawkExternalTool], which is now deprecated. Has the tool been updated since BizHawk 2.4?"
-						: "The assembly doesn't contain a class implementing IExternalToolForm and annotated with [ExternalTool].",
+					ExternalToolAttribute.MissingException => "The assembly doesn't contain a class implementing IExternalToolForm and annotated with [ExternalTool].",
 					ReflectionTypeLoadException => "Something went wrong while trying to load the assembly.",
 					_ => $"An exception of type {e.GetType().FullName} was thrown while trying to load the assembly and look for an IExternalToolForm:\n{e.Message}"
 				};