diff --git a/guix-data-service/web/server.scm b/guix-data-service/web/server.scm
index 5507346..cced889 100644
--- a/guix-data-service/web/server.scm
+++ b/guix-data-service/web/server.scm
@@ -361,6 +361,21 @@ port. Also, the port used can be changed by passing the --port option.\n"
                                           render-metrics)))))
                          #:unwind? #t))
                      #:connection-buffer-size (expt 2 14)
+                     #:post-request-hook
+                     (lambda* (request #:key read-request-time
+                                       response-end-time
+                                       #:allow-other-keys)
+                       (let ((request-duration
+                              (/ (- response-end-time
+                                    read-request-time)
+                                 internal-time-units-per-second)))
+                         (when (> request-duration
+                                  30)
+                           (format
+                            (current-error-port)
+                            "warning: ~a took ~f seconds to complete\n"
+                            (uri-path (request-uri request))
+                            request-duration))))
                      #:host host
                      #:port port)))
                 #:unwind? #t)))