diff --git a/admin/admin.el b/admin/admin.el
index d032c1ceb85..704c38d6f91 100644
--- a/admin/admin.el
+++ b/admin/admin.el
@@ -665,6 +665,7 @@ style=\"text-align:left\">")
 
 (defconst make-manuals-dist-output-variables
   '(("@\\(top_\\)?srcdir@" . ".")	; top_srcdir is wrong, but not used
+    ("@abs_top_builddir@" . "../../")   ; only for in-tree builds
     ("^\\(\\(?:texinfo\\|buildinfo\\|emacs\\)dir *=\\).*" . "\\1 .")
     ("^\\(clean:.*\\)" . "\\1 infoclean")
     ("@MAKEINFO@" . "makeinfo")