diff --git a/Common.ruleset b/Common.ruleset
index fa3401f545..b53ccc1aa3 100644
--- a/Common.ruleset
+++ b/Common.ruleset
@@ -32,9 +32,6 @@
 		<!-- Mark assemblies with assembly version -->
 		<Rule Id="CA1016" Action="Hidden" />
 
-		<!-- Mark attributes with AttributeUsageAttribute -->
-		<Rule Id="CA1018" Action="Hidden" />
-
 		<!-- Enum Storage should be Int32 -->
 		<Rule Id="CA1028" Action="Hidden" />
 
diff --git a/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs b/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
index 098c6683d7..6151de41b5 100644
--- a/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
+++ b/src/BizHawk.Client.Common/Api/ExternalToolAttributes.cs
@@ -118,6 +118,7 @@ namespace BizHawk.Client.Common
 		}
 	}
 
+	[AttributeUsage(AttributeTargets.Class)]
 	public sealed class ExternalToolEmbeddedIconAttribute : Attribute
 	{
 		/// <remarks>The full path, including the assembly name.</remarks>