1 files changed, 1 insertions, 1 deletions

diff --git a/src/WixToolset.Core/CommandLine/CommandLineParser.cs b/src/WixToolset.Core/CommandLine/CommandLineParser.cs
index 017810e0..3c7f3d1e 100644
--- a/src/WixToolset.Core/CommandLine/CommandLineParser.cs
+++ b/src/WixToolset.Core/CommandLine/CommandLineParser.cs
@@ -54,7 +54,7 @@ namespace WixToolset.Core.CommandLine
 
             if (!String.IsNullOrEmpty(context.Arguments))
             {
-                args = CommandLineParser.ParseArgumentsToArray(context.Arguments).Union(args).ToArray();
+                args = CommandLineParser.ParseArgumentsToArray(context.Arguments).Concat(args).ToArray();
             }
 
             return this.ParseStandardCommandLine(context, args);