diff --git a/src/aig/gia/giaSweeper.c b/src/aig/gia/giaSweeper.c
index 7059ba897..735abf30a 100644
--- a/src/aig/gia/giaSweeper.c
+++ b/src/aig/gia/giaSweeper.c
@@ -757,6 +757,8 @@ static Vec_Int_t * Gia_ManGetCex( Gia_Man_t * pGia, Vec_Int_t * vId2Lit, sat_sol
     Vec_IntClear( vCex );
     Gia_ManForEachPi( pGia, pObj, i )
     {
+        if ( Gia_ObjId(pGia, pObj) >= Vec_IntSize(vId2Lit) )
+            continue;
         LitSat = Vec_IntEntry( vId2Lit, Gia_ObjId(pGia, pObj) );
         if ( LitSat == 0 )
         {