diff --git a/src/client/inc/tscUtil.h b/src/client/inc/tscUtil.h
index f14cd8f9e2..690ec2c277 100644
--- a/src/client/inc/tscUtil.h
+++ b/src/client/inc/tscUtil.h
@@ -213,7 +213,7 @@ SExprInfo* tscExprUpdate(SQueryInfo* pQueryInfo, int32_t index, int16_t function
                            int16_t size);
 
 size_t     tscNumOfExprs(SQueryInfo* pQueryInfo);
-size_t     tscExprTopBottomIndex(SQueryInfo* pQueryInfo);
+int32_t     tscExprTopBottomIndex(SQueryInfo* pQueryInfo);
 SExprInfo *tscExprGet(SQueryInfo* pQueryInfo, int32_t index);
 int32_t    tscExprCopy(SArray* dst, const SArray* src, uint64_t uid, bool deepcopy);
 int32_t    tscExprCopyAll(SArray* dst, const SArray* src, bool deepcopy);
diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index 63ce5ebf2c..bb871488fc 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -5864,7 +5864,7 @@ int32_t validateOrderbyNode(SSqlCmd* pCmd, SQueryInfo* pQueryInfo, SSqlNode* pSq
         pQueryInfo->order.orderColId = pSchema[index.columnIndex].colId;
       } else if (isTopBottomQuery(pQueryInfo)) {
         /* order of top/bottom query in interval is not valid  */
-        size_t pos = tscExprTopBottomIndex(pQueryInfo);
+        int32_t pos = tscExprTopBottomIndex(pQueryInfo);
         assert(pos > 0);
         SExprInfo* pExpr = tscExprGet(pQueryInfo, pos - 1);
         assert(pExpr->base.functionId == TSDB_FUNC_TS);
@@ -5951,7 +5951,7 @@ int32_t validateOrderbyNode(SSqlCmd* pCmd, SQueryInfo* pQueryInfo, SSqlNode* pSq
         }
       } else {
         /* order of top/bottom query in interval is not valid  */
-        size_t pos = tscExprTopBottomIndex(pQueryInfo);
+        int32_t pos = tscExprTopBottomIndex(pQueryInfo);
         assert(pos > 0);
         SExprInfo* pExpr = tscExprGet(pQueryInfo, pos - 1);
         assert(pExpr->base.functionId == TSDB_FUNC_TS);
diff --git a/src/client/src/tscUtil.c b/src/client/src/tscUtil.c
index 72791568ba..c5aedf1b71 100644
--- a/src/client/src/tscUtil.c
+++ b/src/client/src/tscUtil.c
@@ -2427,10 +2427,12 @@ size_t tscNumOfExprs(SQueryInfo* pQueryInfo) {
   return taosArrayGetSize(pQueryInfo->exprList);
 }
 
-size_t tscExprTopBottomIndex(SQueryInfo* pQueryInfo){
+int32_t tscExprTopBottomIndex(SQueryInfo* pQueryInfo){
   size_t numOfExprs = tscNumOfExprs(pQueryInfo);
-  for(int32_t i = 0; i < numOfExprs; ++i) {
+  for(size_t i = 0; i < numOfExprs; ++i) {
     SExprInfo* pExpr = tscExprGet(pQueryInfo, i);
+    if (pExpr == NULL)
+      continue;
     if (pExpr->base.functionId == TSDB_FUNC_TOP || pExpr->base.functionId == TSDB_FUNC_BOTTOM) {
       return i;
     }
diff --git a/tests/pytest/functions/function_top.py b/tests/pytest/functions/function_top.py
index 9824afc19f..03a00d918a 100644
--- a/tests/pytest/functions/function_top.py
+++ b/tests/pytest/functions/function_top.py
@@ -132,7 +132,7 @@ class TDTestCase:
         tdSql.checkData(0, 1, "2018-09-17 09:00:00.008")
         tdSql.checkData(1, 0, "2018-09-17 09:00:00.009")
         tdSql.checkData(1, 3, "2018-09-17 09:00:00.009")
-        
+
         #TD-2563 top + super_table + interval 
         tdSql.execute("create table meters(ts timestamp, c int) tags (d int)") 
         tdSql.execute("create table t1 using meters tags (1)")