diff --git a/.editorconfig b/.editorconfig
index 293df0f9e7..1dcc8d7ee8 100644
--- a/.editorconfig
+++ b/.editorconfig
@@ -1103,6 +1103,9 @@ dotnet_diagnostic.RCS1218.severity = warning
 # Use pattern matching instead of combination of 'is' operator and cast operator.
 dotnet_diagnostic.RCS1220.severity = warning
 
+# Make class sealed.
+dotnet_diagnostic.RCS1225.severity = warning
+
 # Unnecessary explicit use of enumerator.
 dotnet_diagnostic.RCS1230.severity = warning
 
diff --git a/OpenRA.Mods.Common/UpdateRules/UpdatePath.cs b/OpenRA.Mods.Common/UpdateRules/UpdatePath.cs
index 99b4027001..a706c8928a 100644
--- a/OpenRA.Mods.Common/UpdateRules/UpdatePath.cs
+++ b/OpenRA.Mods.Common/UpdateRules/UpdatePath.cs
@@ -15,7 +15,7 @@ using OpenRA.Mods.Common.UpdateRules.Rules;
 
 namespace OpenRA.Mods.Common.UpdateRules
 {
-	public class UpdatePath
+	public sealed class UpdatePath
 	{
 		// Define known update paths from stable tags to the current bleed tip
 		//
diff --git a/OpenRA.Mods.D2k/UtilityCommands/D2kMapImporter.cs b/OpenRA.Mods.D2k/UtilityCommands/D2kMapImporter.cs
index 70d19fdbd2..9f18e38bad 100644
--- a/OpenRA.Mods.D2k/UtilityCommands/D2kMapImporter.cs
+++ b/OpenRA.Mods.D2k/UtilityCommands/D2kMapImporter.cs
@@ -18,7 +18,7 @@ using OpenRA.Primitives;
 
 namespace OpenRA.Mods.D2k.UtilityCommands
 {
-	public class D2kMapImporter
+	public sealed class D2kMapImporter
 	{
 		const int MapCordonWidth = 2;