diff --git a/C/unify.c b/C/unify.c
index 0a0841e22..eee30a50a 100644
--- a/C/unify.c
+++ b/C/unify.c
@@ -578,6 +578,7 @@ InitReverseLookupOpcode(void)
       }
     }
   }
+  bzero(OP_RTABLE, sz);
   opeptr = OP_RTABLE;
   /* clear up table */
   {