diff --git a/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs b/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
index 26ff9244cc0..fdb03ebbf83 100644
--- a/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
+++ b/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
@@ -95,8 +95,6 @@ public override bool NotApplicableTo(string romHash, string? sysID)
 
 	public abstract class ExternalToolApplicabilityAttributeBase : Attribute
 	{
-		protected static readonly BizHawkSystemIdToEnumConverter SystemIdConverter = new();
-
 		public abstract bool NotApplicableTo(string sysID);
 
 		public abstract bool NotApplicableTo(string romHash, string? sysID);