diff --git a/src/base/abci/abcRec2.c b/src/base/abci/abcRec2.c
index 352cf0e5c..c84ea3ea1 100644
--- a/src/base/abci/abcRec2.c
+++ b/src/base/abci/abcRec2.c
@@ -1552,6 +1552,7 @@ timeBuild = clock();
     }
 
     // build the node and compute its truth table
+    assert( Vec_PtrSize(vNodes) > 0 );
     nNodesBeg = Gia_ManObjNum( pAig );
     Vec_PtrForEachEntryStart( If_Obj_t *, vNodes, pIfObj, i, nLeaves )
     {