diff --git a/src/base/abc/abcNtk.c b/src/base/abc/abcNtk.c
index 1b823cf00..9d6c4f0ea 100644
--- a/src/base/abc/abcNtk.c
+++ b/src/base/abc/abcNtk.c
@@ -1565,19 +1565,19 @@ void Abc_NtkFixNonDrivenNets( Abc_Ntk_t * pNtk )
 
     // special case
     pNet = Abc_NtkFindNet( pNtk, "$false" );
-    if ( pNet != NULL )
+    if ( pNet != NULL && !Abc_ObjFaninNum(pNet) )
     {
         pNode = Abc_NtkCreateNodeConst0( pNtk );
         Abc_ObjAddFanin( pNet, pNode );
     }
     pNet = Abc_NtkFindNet( pNtk, "$undef" );
-    if ( pNet != NULL )
+    if ( pNet != NULL && !Abc_ObjFaninNum(pNet) )
     {
         pNode = Abc_NtkCreateNodeConst0( pNtk );
         Abc_ObjAddFanin( pNet, pNode );
     }
     pNet = Abc_NtkFindNet( pNtk, "$true" );
-    if ( pNet != NULL )
+    if ( pNet != NULL && !Abc_ObjFaninNum(pNet) )
     {
         pNode = Abc_NtkCreateNodeConst1( pNtk );
         Abc_ObjAddFanin( pNet, pNode );