diff --git a/guix/build/gnu-build-system.scm b/guix/build/gnu-build-system.scm
index 66edd2de2d..fca77f474c 100644
--- a/guix/build/gnu-build-system.scm
+++ b/guix/build/gnu-build-system.scm
@@ -170,7 +170,8 @@ working directory."
             (when command
               (invoke command "--decompress" name)))))
         ;; Attempt to change into child directory.
-        (and=> (first-subdirectory ".") chdir))))
+        (and=> (first-subdirectory ".") chdir)))
+  (for-each make-file-writable (find-files ".")))
 
 (define* (bootstrap #:key bootstrap-scripts
                     #:allow-other-keys)