diff --git a/src/client/src/tscSQLParser.c b/src/client/src/tscSQLParser.c
index 0a52a4fc65b3dceab8be588acfb4863fd1f82a63..b40b879daf22840777101e10d12972028b358835 100644
--- a/src/client/src/tscSQLParser.c
+++ b/src/client/src/tscSQLParser.c
@@ -4744,10 +4744,12 @@ static int32_t validateJsonTagExpr(tSqlExpr* pExpr, char* msgBuf) {
       if(!taosMbsToUcs4(pRight->value.pz, pRight->value.nLen, newData, TSDB_MAX_JSON_TAGS_LEN, &len)){
         tscError("json where condition mbsToUcs4 error");
       }
-      pRight->value.pz = realloc(pRight->value.pz, len);
+      if(len > 0){
+        pRight->value.pz = realloc(pRight->value.pz, len);
+        memcpy(pRight->value.pz, newData, len);
+      }
       pRight->value.nLen = len;
       pRight->value.nType = TSDB_DATA_TYPE_NCHAR;
-      memcpy(pRight->value.pz, newData, len);
     }
   }