diff --git a/doc/guix.texi b/doc/guix.texi
index a512f7dda9..09c7faf254 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -308,6 +308,12 @@ This creates @file{/gnu/store} (@pxref{The Store}) and @file{/var/guix}.
 The latter contains a ready-to-use profile for @code{root} (see next
 step.)
 
+Some versions of GNU@tie{}tar raise a warning about ``implausibly old
+time stamps''.  This is because all the files in the archive have their
+modification time set to zero (which means January 1st, 1970.)  This is
+done on purpose to make sure the archive content is independent of its
+creation time, thus making it reproducible.
+
 Do @emph{not} unpack the tarball on a working Guix system since that
 would overwrite its own essential files.