diff --git a/build-aux/config.sh b/build-aux/config.sh
index a4b9fdef..4fa84441 100644
--- a/build-aux/config.sh
+++ b/build-aux/config.sh
@@ -17,6 +17,7 @@
 # along with GNU Mes.  If not, see <http://www.gnu.org/licenses/>.
 
 srcdir=${srcdir-.}
+top_builddir=${top_builddir-.}
 if [ "$V" = 2 ]; then
     echo $0
     echo srcdest=${srcdest}