1 files changed, 1 insertions, 1 deletions

diff --git a/src/WixToolset.Extensibility/IExtensionCommandLine.cs b/src/WixToolset.Extensibility/IExtensionCommandLine.cs
index 2c7d0a7e..f7b19955 100644
--- a/src/WixToolset.Extensibility/IExtensionCommandLine.cs
+++ b/src/WixToolset.Extensibility/IExtensionCommandLine.cs
@@ -15,7 +15,7 @@ namespace WixToolset.Extensibility
         /// Gets the supported command line types for this extension.
         /// </summary>
         /// <value>The supported command line types for this extension.</value>
-        IEnumerable<ExtensionCommandLineSwitch> CommandLineSwitches { get; }
+        IReadOnlyCollection<ExtensionCommandLineSwitch> CommandLineSwitches { get; }
 
         /// <summary>
         /// Called before the command-line is parsed.