diff --git a/guix/status.scm b/guix/status.scm
index cbea4151f2..4dcbcb0c1f 100644
--- a/guix/status.scm
+++ b/guix/status.scm
@@ -717,6 +717,7 @@ The second return value is a thunk to retrieve the current state."
       (pointer->bytevector ptr count)))
 
   (define (write! bv offset count)
+    (pk 'write count '<> %build-output-pid %build-output-left)
     (if %build-output-pid
         (let ((keep (min count %build-output-left)))
           (set! %build-output