diff --git make-ca-clean/make-ca make-ca-workdir/make-ca
index 437b1b9..2fa235c 100644
--- make-ca-clean/make-ca
+++ make-ca-workdir/make-ca
@@ -16,7 +16,7 @@ VERSION="1.16.1"
 MAKE_CA_CONF="/etc/make-ca.conf"
 
 # CA root for hg.mozilla.org
-MOZILLA_CA_ROOT="/etc/make-ca/ISRG_Root_X1.pem"
+MOZILLA_CA_ROOT="${MOZILLA_CERT_SYSROOT}/etc/make-ca/ISRG_Root_X1.pem"
 
 # Get/set defaults
 if test -f "${MAKE_CA_CONF}"; then