diff --git a/astra-sim-alibabacloud/astra-sim/system/MockNcclGroup.cc b/astra-sim-alibabacloud/astra-sim/system/MockNcclGroup.cc
index 4daf68d5..76aa2fa3 100644
--- a/astra-sim-alibabacloud/astra-sim/system/MockNcclGroup.cc
+++ b/astra-sim-alibabacloud/astra-sim/system/MockNcclGroup.cc
@@ -1598,7 +1598,7 @@ namespace MockNccl {
               result[std::make_pair(ring_id, g_flow_id)] = tmp_result;
               g_flow_id++;
               prevranks.clear();
-              if(rank_it->first){
+              if(rank_it->first!=-1){
                 prevranks = {rank_it->first};
               }
               tmp_result = SingleFlow(
@@ -2100,4 +2100,4 @@ namespace MockNccl {
     return info;
     }
   }
-}
\ No newline at end of file
+}