diff --git a/C/unify.c b/C/unify.c
index 9a5a3c959..76d9a1616 100644
--- a/C/unify.c
+++ b/C/unify.c
@@ -109,7 +109,7 @@ loop:
     derefa_body(d0, ptd0, rtree_loop_unk, rtree_loop_nvar);
   }
   /* Do we still have compound terms to visit */
-  if (to_visit > to_visit0) {
+  if (to_visit < to_visit0) {
     pt0 = to_visit[0];
     pt0_end = to_visit[1];
     *pt0 = (CELL)to_visit[2];
@@ -120,7 +120,7 @@ loop:
 
 cufail:
   /* we found an infinite term */
-  while (to_visit > to_visit) {
+  while (to_visit < to_visit0) {
     CELL *pt0;
     pt0 = to_visit[0];
     *pt0 = (CELL)to_visit[2];
diff --git a/changes-5.1.html b/changes-5.1.html
index ff8ac9cd6..a8cc1532d 100644
--- a/changes-5.1.html
+++ b/changes-5.1.html
@@ -16,6 +16,7 @@
 
 <h2>Yap-5.1.2:</h2>
 <ul>
+<li> NEW:  unify_with_occurs_check was very broken (obs from Aline Paes).</li> 
 <li> NEW:  partial support for UNICODE.</li> 
 <li> FIXED:  &yuml; has ISO-LATIN1 code 255, so it would be confused with EOF
 (obs from Miguel Filgueiras).</li>