diff --git a/src/Microsoft.DotNet.XHarness.CLI/Commands/WebServer.cs b/src/Microsoft.DotNet.XHarness.CLI/Commands/WebServer.cs
index 3b473c2d20356..ddfcc4a923672 100644
--- a/src/Microsoft.DotNet.XHarness.CLI/Commands/WebServer.cs
+++ b/src/Microsoft.DotNet.XHarness.CLI/Commands/WebServer.cs
@@ -123,6 +123,8 @@ public void Configure(IApplicationBuilder app, IOptionsMonitor<TestWebServerOpti
             {
                 var provider = new FileExtensionContentTypeProvider();
                 provider.Mappings[".wasm"] = "application/wasm";
+                provider.Mappings[".cjs"] = "text/javascript";
+                provider.Mappings[".mjs"] = "text/javascript";
 
                 foreach (var extn in new string[] { ".dll", ".pdb", ".dat", ".blat" })
                 {