1 files changed, 1 insertions, 1 deletions

diff --git a/src/wixext/FirewallExtensionFactory.cs b/src/wixext/FirewallExtensionFactory.cs
index 377ae0ee..279b322a 100644
--- a/src/wixext/FirewallExtensionFactory.cs
+++ b/src/wixext/FirewallExtensionFactory.cs
@@ -8,7 +8,7 @@ namespace WixToolset.Firewall
 
     public class FirewallExtensionFactory : BaseExtensionFactory
     {
-        protected override IEnumerable<Type> ExtensionTypes => new[]
+        protected override IReadOnlyCollection<Type> ExtensionTypes => new[]
         {
             typeof(FirewallCompiler),
             typeof(FirewallExtensionData),