diff --git a/be/src/vec/olap/olap_data_convertor.cpp b/be/src/vec/olap/olap_data_convertor.cpp
index 58ab5d6579..33598c4e98 100644
--- a/be/src/vec/olap/olap_data_convertor.cpp
+++ b/be/src/vec/olap/olap_data_convertor.cpp
@@ -160,6 +160,7 @@ void OlapBlockDataConvertor::OlapColumnDataConvertorBase::set_source_column(
 void OlapBlockDataConvertor::OlapColumnDataConvertorBase::clear_source_column() {
     // just to reduce the source column's ref count to 1
     _typed_column.column = nullptr;
+    _nullmap = nullptr;
 }
 
 // This should be called only in SegmentWriter. If you want to access nullmap in Convertor,