diff --git a/src/sat/sat_model_converter.cpp b/src/sat/sat_model_converter.cpp
index 05c89fba7..fac4cface 100644
--- a/src/sat/sat_model_converter.cpp
+++ b/src/sat/sat_model_converter.cpp
@@ -46,7 +46,7 @@ namespace sat {
             UNREACHABLE();
             throw solver_exception("flipping assumption");
         }
-        if (m_solver && m_solver->is_external(v)) {
+        if (m_solver && m_solver->is_external(v) && m_solver->is_incremental()) {
             std::cout << "flipping external v" << v << "\n";
             UNREACHABLE();
             throw solver_exception("flipping external");
diff --git a/src/sat/sat_simplifier.cpp b/src/sat/sat_simplifier.cpp
index 6d578b4f9..c101e3a29 100644
--- a/src/sat/sat_simplifier.cpp
+++ b/src/sat/sat_simplifier.cpp
@@ -970,11 +970,12 @@ namespace sat {
         }
 
         void insert(literal l) {
+            VERIFY(process_var(l.var()));
             m_queue.insert(l);
         }
 
         bool process_var(bool_var v) {
-            return !s.s.is_assumption(v) &&  !s.was_eliminated(v) && !s.is_external(v);
+            return !s.s.is_assumption(v) && !s.was_eliminated(v) && !s.is_external(v);
         }
 
         void operator()() {