diff --git a/src/client/src/tscFunctionImpl.c b/src/client/src/tscFunctionImpl.c
index 62e55c033f53b53aaf9035b2c7196ffe7faef522..7d41d57cccb5330de33f15e23c0d4bdad5515383 100644
--- a/src/client/src/tscFunctionImpl.c
+++ b/src/client/src/tscFunctionImpl.c
@@ -2222,7 +2222,8 @@ static void buildTopBotStruct(STopBotInfo *pTopBotInfo, SQLFunctionCtx *pCtx) {
   tmp += POINTER_BYTES * pCtx->param[0].i64Key;
   
   size_t size = sizeof(tValuePair) + pCtx->tagInfo.tagsLen;
-  
+  assert(pCtx->param[0].i64Key > 0);
+
   for (int32_t i = 0; i < pCtx->param[0].i64Key; ++i) {
     pTopBotInfo->res[i] = (tValuePair*) tmp;
     pTopBotInfo->res[i]->pTags = tmp + sizeof(tValuePair);