diff --git a/guix/derivations.scm b/guix/derivations.scm
index 140c22b620d861592a59667ae5ad97a284650699..706c6504694e2cec1b54f9fd8e51b4336ef6696a 100644
--- a/guix/derivations.scm
+++ b/guix/derivations.scm
@@ -622,7 +622,7 @@ (define (write-env-var env-var port)
      (display ")" port))))
 
 (define derivation->bytevector
-  (mlambda (drv)
+  (lambda (drv)
     "Return the external representation of DRV as a UTF-8-encoded string."
     (with-fluids ((%default-port-encoding "UTF-8"))
       (call-with-values open-bytevector-output-port