diff --git a/backend/src/Squidex.Web/Pipeline/AppResolver.cs b/backend/src/Squidex.Web/Pipeline/AppResolver.cs
index ea0976033..4e5d43cae 100644
--- a/backend/src/Squidex.Web/Pipeline/AppResolver.cs
+++ b/backend/src/Squidex.Web/Pipeline/AppResolver.cs
@@ -81,6 +81,7 @@ namespace Squidex.Web.Pipeline
                 }
 
                 context.HttpContext.Features.Set<IAppFeature>(new AppFeature(app.NamedId()));
+                context.HttpContext.Response.Headers.Add("X-AppId", app.Id.ToString());
             }
 
             await next();