diff --git a/guix-data-service/web/controller.scm b/guix-data-service/web/controller.scm
index a20e761..5d0a651 100644
--- a/guix-data-service/web/controller.scm
+++ b/guix-data-service/web/controller.scm
@@ -719,8 +719,8 @@
    #:on-error 'backtrace
    #:post-error (lambda args
                   (case (most-appropriate-mime-type
-                         '(application/json text/html)
-                         mime-types)
+                         mime-types
+                         '(text/html application/json))
                     ((application/json)
                      (render-json `((error . ,(if (%show-error-details)
                                                   (simple-format #f "~A" args)