diff --git a/util/postinstall.sh.in b/util/postinstall.sh.in
index 35b72b5..8ec4604 100755
--- a/util/postinstall.sh.in
+++ b/util/postinstall.sh.in
@@ -381,7 +381,7 @@
    echo "Done."
 
    echo "Fix piler.conf path in pilerpurge.py"
-   sed "s%\/etc\/piler\/piler\.conf%${SYSCONFDIR}\/piler\/piler\.conf%" "${LIBEXECDIR}/piler/pilerpurge.py"
+   sed -i "s%\/etc\/piler\/piler\.conf%${SYSCONFDIR}\/piler\/piler\.conf%" "${LIBEXECDIR}/piler/pilerpurge.py"
 
    make_certificate