diff --git a/backend/src/Designer/Controllers/PreviewController.cs b/backend/src/Designer/Controllers/PreviewController.cs
index 2f62caf0af0..d91cd2076be 100644
--- a/backend/src/Designer/Controllers/PreviewController.cs
+++ b/backend/src/Designer/Controllers/PreviewController.cs
@@ -194,6 +194,7 @@ public async Task<ActionResult<ApplicationSettings>> ApplicationSettings(string
         /// <param name="cancellationToken">A <see cref="CancellationToken"/> that observes if operation is cancelled.</param>
         /// <returns>layoutsets file, or an OK response if app does not use layoutsets</returns>
         [HttpGet]
+        [UseSystemTextJson]
         [Route("api/layoutsets")]
         public async Task<ActionResult<LayoutSets>> LayoutSets(string org, string app, CancellationToken cancellationToken)
         {