diff --git a/src/or/routerlist.c b/src/or/routerlist.c
index d8c8a81738..2815c60963 100644
--- a/src/or/routerlist.c
+++ b/src/or/routerlist.c
@@ -5207,14 +5207,14 @@ update_consensus_router_descriptor_downloads(time_t now, int is_vote,
     SMARTLIST_FOREACH_BEGIN(no_longer_old, signed_descriptor_t *, sd) {
         const char *msg;
         was_router_added_t r;
+        time_t tmp_cert_expiration_time;
         routerinfo_t *ri = routerlist_reparse_old(rl, sd);
         if (!ri) {
           log_warn(LD_BUG, "Failed to re-parse a router.");
           continue;
         }
-        /* need to compute this now, since add_to_routerlist may free. */
-        char time_cert_expires[ISO_TIME_LEN+1];
-        format_iso_time(time_cert_expires, ri->cert_expiration_time);
+        /* need to remember for below, since add_to_routerlist may free. */
+        tmp_cert_expiration_time = ri->cert_expiration_time;
 
         r = router_add_to_routerlist(ri, &msg, 1, 0);
         if (WRA_WAS_OUTDATED(r)) {
@@ -5224,7 +5224,9 @@ update_consensus_router_descriptor_downloads(time_t now, int is_vote,
                    msg?msg:"???");
           if (r == ROUTER_CERTS_EXPIRED) {
             char time_cons[ISO_TIME_LEN+1];
+            char time_cert_expires[ISO_TIME_LEN+1];
             format_iso_time(time_cons, consensus->valid_after);
+            format_iso_time(time_cert_expires, tmp_cert_expiration_time);
             log_warn(LD_DIR, "  (I'm looking at a consensus from %s; This "
                      "router's certificates began expiring at %s.)",
                      time_cons, time_cert_expires);