diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index fff3c0cc0267812941c330b7d067d5f2ec3e2c31..bb103f23c6718c40ab9933c7ed84a73f3edb70fa 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -6101,7 +6101,7 @@ void tscPrintSelectClause(SSqlObj* pSql, int32_t subClauseIndex) {
     int32_t tmpLen = 0;
     tmpLen =
         sprintf(tmpBuf, "%s(uid:%" PRId64 ", %d)", aAggs[pExpr->functionId].aName, pExpr->uid, pExpr->colInfo.colId);
-    if (tmpLen + offset > totalBufSize) break;
+    if (tmpLen + offset >= totalBufSize - 1) break;
 
     offset += sprintf(str + offset, "%s", tmpBuf);
 
@@ -6110,6 +6110,7 @@ void tscPrintSelectClause(SSqlObj* pSql, int32_t subClauseIndex) {
     }
   }
 
+  assert(offset < totalBufSize);
   str[offset] = ']';
   tscDebug("%p select clause:%s", pSql, str);
 }