diff --git a/src/glpios09.c b/src/glpios09.c
index a6a4e82..bea1fd6 100644
--- a/src/glpios09.c
+++ b/src/glpios09.c
@@ -505,7 +505,9 @@ void ios_pcost_update(glp_tree *tree)
          x[j] in optimal solution to LP relaxation of the parent
          subproblem */
       dx = tree->mip->col[j]->prim - tree->curr->up->br_val;
-      xassert(dx != 0.0);
+      /* if tol_int is smaller than tol_piv times the unscaled variable,
+         dx may be zero or close to it */
+      if (fabs(dx) < tree->parm->tol_int) goto skip;
       /* determine corresponding change dz = new dz - old dz in the
          objective function value */
       dz = tree->mip->obj_val - tree->curr->up->lp_obj;