diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index b28dd9cf1c06ee1f862ef2c585bc888259dab29e..e2573f7e19303966e9f17a2731444bf9fca7ab87 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -4750,7 +4750,7 @@ int32_t setAlterTableInfo(SSqlObj* pSql, struct SSqlInfo* pInfo) {
 
     // validate the length of binary
     if ((pTagsSchema->type == TSDB_DATA_TYPE_BINARY || pTagsSchema->type == TSDB_DATA_TYPE_NCHAR) &&
-        (pVarList->a[1].pVar.nLen + VARSTR_HEADER_SIZE) > pTagsSchema->bytes) {
+        varDataTLen(pAlterSQL->tagData.data) > pTagsSchema->bytes) {
       return invalidSqlErrMsg(tscGetErrorMsgPayload(pCmd), msg14);
     }
 
diff --git a/tests/script/general/parser/tags_dynamically_specifiy.sim b/tests/script/general/parser/tags_dynamically_specifiy.sim
index 0a5d5c971649abae07d149f1cc914eb096e638fa..07bf4d8dd1cae6b0b374b9b67b1dca58f218fb3f 100644
--- a/tests/script/general/parser/tags_dynamically_specifiy.sim
+++ b/tests/script/general/parser/tags_dynamically_specifiy.sim
@@ -96,5 +96,10 @@ if $rows != 14 then
   return -1
 endi
 
+print ===============================> td-1765
+sql create table m1(ts timestamp, k int) tags(a binary(4), b nchar(4));
+sql create table tm0 using m1 tags('abcd', 'abcd');
+sql_error alter table tm0 set tag b = 'abcd1';
+sql_error alter table tm0 set tag a = 'abcd1';
 
 system sh/exec.sh -n dnode1 -s stop -x SIGINT
\ No newline at end of file