1 files changed, 1 insertions, 1 deletions

diff --git a/src/wixext/DifxAppExtensionFactory.cs b/src/wixext/DifxAppExtensionFactory.cs
index 4565ce17..3932685d 100644
--- a/src/wixext/DifxAppExtensionFactory.cs
+++ b/src/wixext/DifxAppExtensionFactory.cs
@@ -8,7 +8,7 @@ namespace WixToolset.DifxApp
 
     public class DifxAppExtensionFactory : BaseExtensionFactory
     {
-        protected override IEnumerable<Type> ExtensionTypes => new[]
+        protected override IReadOnlyCollection<Type> ExtensionTypes => new[]
         {
             typeof(DifxAppCompiler),
             typeof(DifxAppExtensionData),