diff --git a/dbms/src/Functions/IFunction.cpp b/dbms/src/Functions/IFunction.cpp
index 3cd03c5b07c..e41da2e56a8 100644
--- a/dbms/src/Functions/IFunction.cpp
+++ b/dbms/src/Functions/IFunction.cpp
@@ -352,8 +352,6 @@ void IFunction::postProcessResult(Strategy strategy, Block & block, const Block
 		throw Exception{"IFunction: internal error", ErrorCodes::LOGICAL_ERROR};
 }
 
-/// Return a copy of a given block in which the specified columns are replaced by
-/// their respective nested columns if they are nullable.
 Block IFunction::createBlockWithNestedColumns(const Block & block, ColumnNumbers args)
 {
 	std::sort(args.begin(), args.end());
@@ -373,10 +371,10 @@ Block IFunction::createBlockWithNestedColumns(const Block & block, ColumnNumbers
 			if (col.column->isNullable())
 			{
 				auto nullable_col = static_cast<const ColumnNullable *>(col.column.get());
-				ColumnPtr nested_col = nullable_col->getNestedColumn();
+				const ColumnPtr & nested_col = nullable_col->getNestedColumn();
 
 				auto nullable_type = static_cast<const DataTypeNullable *>(col.type.get());
-				DataTypePtr nested_type = nullable_type->getNestedType();
+				const DataTypePtr & nested_type = nullable_type->getNestedType();
 
 				res.insert(i, {nested_col, nested_type, col.name});
 
diff --git a/dbms/src/Storages/MergeTree/MergeTreeData.cpp b/dbms/src/Storages/MergeTree/MergeTreeData.cpp
index baf5dfd4412..490610ebe4e 100644
--- a/dbms/src/Storages/MergeTree/MergeTreeData.cpp
+++ b/dbms/src/Storages/MergeTree/MergeTreeData.cpp
@@ -863,7 +863,7 @@ MergeTreeData::AlterDataPartTransactionPtr MergeTreeData::alterDataPart(
 		if (it.second == "")
 			new_checksums.files.erase(it.first);
 		else
-			new_checksums.files[it.second] = add_checksums.files.at(it.first);
+			new_checksums.files[it.second] = add_checksums.files[it.first];
 	}
 
 	if (new_primary_key_file_size)