diff --git a/guix/build/gnu-build-system.scm b/guix/build/gnu-build-system.scm
index e5f3197b0a..7d92b8d72e 100644
--- a/guix/build/gnu-build-system.scm
+++ b/guix/build/gnu-build-system.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2018 Mark H Weaver <mhw@netris.org>
 ;;;
 ;;; This file is part of GNU Guix.
@@ -784,8 +784,8 @@ in order.  Return #t if all the PHASES succeeded, #f otherwise."
       (+ (time-second diff)
          (/ (time-nanosecond diff) 1e9))))
 
-  (setvbuf (current-output-port) _IOLBF)
-  (setvbuf (current-error-port) _IOLBF)
+  (setvbuf (current-output-port) 'line)
+  (setvbuf (current-error-port) 'line)
 
   ;; Encoding/decoding errors shouldn't be silent.
   (fluid-set! %default-port-conversion-strategy 'error)
diff --git a/guix/build/utils.scm b/guix/build/utils.scm
index cb5621a5a9..a21dbb0128 100644
--- a/guix/build/utils.scm
+++ b/guix/build/utils.scm
@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
 ;;; Copyright © 2013 Andreas Enge <andreas@enge.fr>
 ;;; Copyright © 2013 Nikita Karetnikov <nikita@karetnikov.org>
 ;;; Copyright © 2015, 2018 Mark H Weaver <mhw@netris.org>
@@ -101,7 +101,27 @@
 
             locale-category->string))
 
+
+;;;
+;;; Guile 2.0 compatibility later.
+;;;
 
+;; The bootstrap Guile is Guile 2.0, so provide a compatibility layer.
+(cond-expand
+  ((and guile-2 (not guile-2.2))
+   (define (setvbuf port mode . rest)
+     (apply (@ (guile) setvbuf) port
+            (match mode
+              ('line _IOLBF)
+              ('block _IOFBF)
+              ('none _IONBF)
+              (_ mode))                           ;an _IO* integer
+            rest))
+
+   (module-replace! (current-module) '(setvbuf)))
+  (else #f))
+
+
 ;;;
 ;;; Directories.
 ;;;
@@ -989,8 +1009,8 @@ known as `nuke-refs' in Nixpkgs."
         ;; We cannot use `regexp-exec' here because it cannot deal with
         ;; strings containing NUL characters.
         (format #t "removing store references from `~a'...~%" file)
-        (setvbuf in _IOFBF 65536)
-        (setvbuf out _IOFBF 65536)
+        (setvbuf in 'block 65536)
+        (setvbuf out 'block 65536)
         (fold-port-matches (lambda (match result)
                              (put-bytevector out (string->utf8 store))
                              (put-u8 out (char->integer #\/))