diff --git a/ydb/core/tx/columnshard/engines/reader/common_reader/iterator/fetching.cpp b/ydb/core/tx/columnshard/engines/reader/common_reader/iterator/fetching.cpp
index f22fa8683677..edfcf0c69660 100644
--- a/ydb/core/tx/columnshard/engines/reader/common_reader/iterator/fetching.cpp
+++ b/ydb/core/tx/columnshard/engines/reader/common_reader/iterator/fetching.cpp
@@ -121,7 +121,7 @@ void TFetchingScript::Allocation(const std::set<ui32>& entityIds, const EStageFe
 TString IFetchingStep::DebugString() const {
     TStringBuilder sb;
     sb << "name=" << Name << ";duration=" << GetSumDuration() << ";"
-       << "size=" << 1e-9 * SumSize << ";details={" << DoDebugString() << "};";
+       << "size=" << 1e-9 * GetSumSize() << ";details={" << DoDebugString() << "};";
     return sb;
 }
 
diff --git a/ydb/core/tx/columnshard/engines/reader/common_reader/iterator/fetching.h b/ydb/core/tx/columnshard/engines/reader/common_reader/iterator/fetching.h
index 9e284e2c5a70..de64e8664583 100644
--- a/ydb/core/tx/columnshard/engines/reader/common_reader/iterator/fetching.h
+++ b/ydb/core/tx/columnshard/engines/reader/common_reader/iterator/fetching.h
@@ -68,7 +68,7 @@ class IFetchingStep: public TNonCopyable {
 private:
     YDB_READONLY_DEF(TString, Name);
     TAtomicCounter SumDuration;
-    YDB_READONLY(ui64, SumSize, 0);
+    TAtomicCounter SumSize;
     TFetchingStepSignals Signals;
 
 protected:
@@ -82,12 +82,16 @@ class IFetchingStep: public TNonCopyable {
         return TDuration::MicroSeconds(SumDuration.Val());
     }
 
+    ui64 GetSumSize() const {
+        return SumSize.Val();
+    }
+
     void AddDuration(const TDuration d) {
         SumDuration.Add(d.MicroSeconds());
         Signals.AddDuration(d);
     }
     void AddDataSize(const ui64 size) {
-        SumSize += size;
+        SumSize.Add(size);
         Signals.AddBytes(size);
     }