diff --git a/source/libs/function/src/builtinsimpl.c b/source/libs/function/src/builtinsimpl.c
index 4e1feb75b1..e57b9f9a34 100644
--- a/source/libs/function/src/builtinsimpl.c
+++ b/source/libs/function/src/builtinsimpl.c
@@ -2924,6 +2924,8 @@ static void firstlastSaveTupleData(const SSDataBlock* pSrcBlock, int32_t rowInde
 
   if (!pInfo->hasResult) {
     pInfo->pos = saveTupleData(pCtx, rowIndex, pSrcBlock, NULL);
+    ASSERT(pCtx->subsidiaries.buf != NULL);
+    ASSERT(pCtx->subsidiaries.rowLen > 0);
   } else {
     updateTupleData(pCtx, rowIndex, pSrcBlock, &pInfo->pos);
   }