2 files changed, 2 insertions, 2 deletions

diff --git a/src/wixext/IisExtensionFactory.cs b/src/wixext/IisExtensionFactory.cs
index 038379f8..2fb7e682 100644
--- a/src/wixext/IisExtensionFactory.cs
+++ b/src/wixext/IisExtensionFactory.cs
@@ -8,7 +8,7 @@ namespace WixToolset.Iis
 
     public class IisExtensionFactory : BaseExtensionFactory
     {
-        protected override IEnumerable<Type> ExtensionTypes => new[]
+        protected override IReadOnlyCollection<Type> ExtensionTypes => new[]
         {
             typeof(IIsCompiler),
             typeof(IIsExtensionData),
diff --git a/src/wixext/IisWindowsInstallerBackendBinderExtension.cs b/src/wixext/IisWindowsInstallerBackendBinderExtension.cs
index 29d34a09..a61cbad6 100644
--- a/src/wixext/IisWindowsInstallerBackendBinderExtension.cs
+++ b/src/wixext/IisWindowsInstallerBackendBinderExtension.cs
@@ -8,6 +8,6 @@ namespace WixToolset.Iis
 
     public class IisWindowsInstallerBackendBinderExtension : BaseWindowsInstallerBackendBinderExtension
     {
-        public override IEnumerable<TableDefinition> TableDefinitions => IisTableDefinitions.All;
+        public override IReadOnlyCollection<TableDefinition> TableDefinitions => IisTableDefinitions.All;
     }
 }