diff --git a/C/unify.c b/C/unify.c
index 4e4b7b81d..fa202e011 100644
--- a/C/unify.c
+++ b/C/unify.c
@@ -36,6 +36,7 @@ int
 Yap_rational_tree_loop(CELL *pt0, CELL *pt0_end, CELL **to_visit, CELL **to_visit_max)
 {
 
+  CELL ** base = to_visit;
 rtree_loop:
   while (pt0 < pt0_end) {
     register CELL *ptd0;
@@ -91,7 +92,7 @@ rtree_loop:
     derefa_body(d0, ptd0, rtree_loop_unk, rtree_loop_nvar);
   }
   /* Do we still have compound terms to visit */
-  if (to_visit < (CELL **)to_visit_base) {
+  if (to_visit < base) {
     pt0 = to_visit[0];
     pt0_end = to_visit[1];
     *pt0 = (CELL)to_visit[2];
@@ -102,7 +103,7 @@ rtree_loop:
 
 cufail:
   /* we found an infinite term */
-  while (to_visit < (CELL **)to_visit_base) {
+  while (to_visit < (CELL **)base) {
     CELL *pt0;
     pt0 = to_visit[0];
     *pt0 = (CELL)to_visit[2];