diff --git a/source/dnode/mnode/impl/src/mndIndex.c b/source/dnode/mnode/impl/src/mndIndex.c
index efaff7ffc4..2157804559 100644
--- a/source/dnode/mnode/impl/src/mndIndex.c
+++ b/source/dnode/mnode/impl/src/mndIndex.c
@@ -515,7 +515,6 @@ int32_t mndRetrieveTagIdx(SRpcMsg *pReq, SShowObj *pShow, SSDataBlock *pBlock, i
     if (pDb == NULL) return 0;
   }
   SSmaAndTagIter *pIter = pShow->pIter;
-  int             invalid = -1;
   while (numOfRows < rows) {
     pIter->pIdxIter = sdbFetch(pSdb, SDB_IDX, pIter->pIdxIter, (void **)&pIdx);
     if (pIter->pIdxIter == NULL) break;
@@ -552,7 +551,7 @@ int32_t mndRetrieveTagIdx(SRpcMsg *pReq, SShowObj *pShow, SSDataBlock *pBlock, i
 
     pColInfo = taosArrayGet(pBlock->pDataBlock, cols++);
 
-    colDataSetVal(pColInfo, numOfRows, (const char *)&invalid, false);
+    colDataSetVal(pColInfo, numOfRows, NULL, true);
 
     pColInfo = taosArrayGet(pBlock->pDataBlock, cols++);
     colDataSetVal(pColInfo, numOfRows, (const char *)&pIdx->createdTime, false);
diff --git a/tests/system-test/0-others/show_tag_index.py b/tests/system-test/0-others/show_tag_index.py
index 6c19dbce0d..663426b7ff 100644
--- a/tests/system-test/0-others/show_tag_index.py
+++ b/tests/system-test/0-others/show_tag_index.py
@@ -64,7 +64,7 @@ class TDTestCase:
         tdSql.checkData(0, 0, 'idx1')
         tdSql.checkData(0, 1, 'db')
         tdSql.checkData(0, 2, 'stb')
-        tdSql.checkData(0, 3, -1)
+        tdSql.checkData(0, 3, None)
         tdSql.checkData(0, 5, 't1')
         tdSql.checkData(0, 6, 'tag_index')