diff --git a/src/nlsat/nlsat_solver.cpp b/src/nlsat/nlsat_solver.cpp
index 0ccaa2f2c..0e3bf8c95 100644
--- a/src/nlsat/nlsat_solver.cpp
+++ b/src/nlsat/nlsat_solver.cpp
@@ -734,8 +734,10 @@ namespace nlsat {
         void undo_set_updt(interval_set * old_set) {
             SASSERT(m_xk != null_var);
             var x = m_xk;
-            m_ism.dec_ref(m_infeasible[x]);
-            m_infeasible[x] = old_set;
+			if (x < m_infeasible.size() && m_infeasible[x]) {
+				m_ism.dec_ref(m_infeasible[x]);
+				m_infeasible[x] = old_set;
+			}
         }
 
         void undo_new_stage() {
@@ -757,7 +759,8 @@ namespace nlsat {
 
         void undo_updt_eq(atom * a) {
             SASSERT(m_xk != null_var);
-            m_var2eq[m_xk] = a; 
+			if (m_var2eq.size() > m_xk)
+                m_var2eq[m_xk] = a; 
         }
 
         template<typename Predicate>
diff --git a/src/tactic/smtlogics/qfnia_tactic.cpp b/src/tactic/smtlogics/qfnia_tactic.cpp
index f0a4ceb57..3b890b632 100644
--- a/src/tactic/smtlogics/qfnia_tactic.cpp
+++ b/src/tactic/smtlogics/qfnia_tactic.cpp
@@ -107,8 +107,8 @@ tactic * mk_qfnia_tactic(ast_manager & m, params_ref const & p) {
     simp_p.set_bool("som", true); // expand into sums of monomials
 
     return and_then(mk_qfnia_premable(m, p),
-                    or_else(mk_qfnia_sat_solver(m, p),
-                            mk_qfnia_nlsat_solver(m, p),
+                    or_else(mk_qfnia_nlsat_solver(m, p),
+                            mk_qfnia_sat_solver(m, p),
                             and_then(using_params(mk_simplify_tactic(m), simp_p),
                                      mk_smt_tactic())));
 }