diff --git a/src/query/src/qFilter.c b/src/query/src/qFilter.c
index 4f2543030bb7089c55cd6472a6957db286fc4ad9..c7a7ea963d5635c76030d2199ac99a60924d99a7 100644
--- a/src/query/src/qFilter.c
+++ b/src/query/src/qFilter.c
@@ -1113,7 +1113,10 @@ int32_t filterConvertSetFromBinary(void **q, const char *buf, int32_t len, uint3
         }
         t = varDataLen(tmp);
         pvar = varDataVal(tmp);
-        strntolower_s(pvar, pvar, t);
+        
+        if (tolower) {
+          strntolower_s(pvar, pvar, (int32_t)t);
+        }
         break;
       }
       case TSDB_DATA_TYPE_NCHAR: {
diff --git a/tests/pytest/query/isNullTest.py b/tests/pytest/query/isNullTest.py
index 7b79679c7d9d9ac4629a69b32acb1a11b61a83c1..f9fbb47715043fb63a51fbb127cb7a889883fafb 100644
--- a/tests/pytest/query/isNullTest.py
+++ b/tests/pytest/query/isNullTest.py
@@ -66,7 +66,7 @@ class TDTestCase:
         tdSql.checkData(0, 0, 12)
 
         tdSql.query("select count(*) from st where t2 <> '' ")
-        tdSql.checkData(0, 0, 24)
+        tdSql.checkData(0, 0, 12)
 
         tdSql.query("select count(*) from st where t3 is null")
         tdSql.checkData(0, 0, 12)
@@ -81,7 +81,7 @@ class TDTestCase:
         tdSql.checkData(0, 0, 12)
 
         tdSql.query("select count(*) from st where t3 <> '' ")
-        tdSql.checkData(0, 0, 24)
+        tdSql.checkData(0, 0, 12)
 
         tdSql.query("select count(*) from st where c1 is not null")
         tdSql.checkData(0, 0, 30)