diff --git a/dbms/include/DB/Functions/IFunction.h b/dbms/include/DB/Functions/IFunction.h
index 2694f0a55f2..45660b2258b 100644
--- a/dbms/include/DB/Functions/IFunction.h
+++ b/dbms/include/DB/Functions/IFunction.h
@@ -141,7 +141,7 @@ protected:
 	/// Returns the copy of a given block in which each column specified in
 	/// the "arguments" parameter is replaced with its respective nested
 	/// column if it is nullable.
-	static Block extractNonNullableBlock(const Block & block, const ColumnNumbers & arguments);
+	static Block extractNonNullableBlock(const Block & block, const ColumnNumbers args);
 
 private:
 	/// Internal method used for implementing both the execute() methods.
diff --git a/dbms/src/Functions/FunctionsConditional.cpp b/dbms/src/Functions/FunctionsConditional.cpp
index 5a2dc34781d..fb044c2aba2 100644
--- a/dbms/src/Functions/FunctionsConditional.cpp
+++ b/dbms/src/Functions/FunctionsConditional.cpp
@@ -208,22 +208,22 @@ void FunctionMultiIf::executeImpl(Block & block, const ColumnNumbers & args, siz
 		{
 			/// Keep track of which columns are nullable.
 			std::vector<UInt8> nullable_cols_map;
-			nullable_cols_map.reserve(args.size());
+			nullable_cols_map.resize(args.size());
 			for (const auto & arg : args)
 			{
 				const auto & col = block.unsafeGetByPosition(arg).column;
 				bool may_have_null = col->isNullable();
-				nullable_cols_map.push_back(static_cast<UInt8>(may_have_null));
+				nullable_cols_map[arg] = may_have_null ? 1 : 0;
 			}
 
 			/// Keep track of which columns are null.
 			std::vector<UInt8> null_cols_map;
-			null_cols_map.reserve(args.size());
+			null_cols_map.resize(args.size());
 			for (const auto & arg : args)
 			{
 				const auto & col = block.unsafeGetByPosition(arg).column;
 				bool has_null = col->isNull();
-				null_cols_map.push_back(static_cast<UInt8>(has_null));
+				null_cols_map[arg] = has_null ? 1 : 0;
 			}
 
 			auto null_map = std::make_shared<ColumnUInt8>(row_count);
diff --git a/dbms/src/Functions/IFunction.cpp b/dbms/src/Functions/IFunction.cpp
index 0808d4b99ad..736801b131d 100644
--- a/dbms/src/Functions/IFunction.cpp
+++ b/dbms/src/Functions/IFunction.cpp
@@ -11,20 +11,20 @@ namespace DB
 namespace
 {
 
-void createNullValuesByteMap(Block & block, size_t result)
+void createNullValuesByteMap(Block & block, const ColumnNumbers & args, size_t result)
 {
 	ColumnNullable & res_col = static_cast<ColumnNullable &>(*block.unsafeGetByPosition(result).column);
 
-	for (size_t i = 0; i < block.columns(); ++i)
+	for (const auto & arg : args)
 	{
-		if (i == result)
+		if (arg == result)
 			continue;
 
-		const ColumnWithTypeAndName & elem = block.unsafeGetByPosition(i);
+		const ColumnWithTypeAndName & elem = block.unsafeGetByPosition(arg);
 		if (elem.column && elem.column.get()->isNullable())
 		{
-			const ColumnNullable & concrete_col = static_cast<const ColumnNullable &>(*elem.column);
-			res_col.updateNullValuesByteMap(concrete_col);
+			const ColumnNullable & nullable_col = static_cast<const ColumnNullable &>(*elem.column);
+			res_col.updateNullValuesByteMap(nullable_col);
 		}
 	}
 }
@@ -198,19 +198,19 @@ void IFunction::getLambdaArgumentTypes(DataTypes & arguments) const
 		getLambdaArgumentTypesImpl(arguments);
 }
 
-Block IFunction::extractNonNullableBlock(const Block & block, const ColumnNumbers & arguments)
+/// 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::extractNonNullableBlock(const Block & block, const ColumnNumbers args)
 {
+	std::sort(args.begin(), args.end());
+
 	Block non_nullable_block;
 
-	ColumnNumbers args2 = arguments;
-	std::sort(args2.begin(), args2.end());
-
-	size_t pos = 0;
 	for (size_t i = 0; i < block.columns(); ++i)
 	{
 		const auto & col = block.unsafeGetByPosition(i);
 
-		bool found = std::binary_search(args2.begin(), args2.end(), pos) && col.column && col.type;
+		bool found = std::binary_search(args.begin(), args.end(), i) && col.column && col.type;
 
 		if (found && col.column.get()->isNullable())
 		{
@@ -220,12 +220,10 @@ Block IFunction::extractNonNullableBlock(const Block & block, const ColumnNumber
 			auto nullable_type = static_cast<const DataTypeNullable *>(col.type.get());
 			DataTypePtr nested_type = nullable_type->getNestedType();
 
-			non_nullable_block.insert(pos, {nested_col, nested_type, col.name});
+			non_nullable_block.insert(i, {nested_col, nested_type, col.name});
 		}
 		else
-			non_nullable_block.insert(pos, col);
-
-		++pos;
+			non_nullable_block.insert(i, col);
 	}
 
 	return non_nullable_block;
@@ -249,8 +247,8 @@ void IFunction::perform(Block & block, const ColumnNumbers & arguments, size_t r
 		ColumnWithTypeAndName & dest_col = block.getByPosition(result);
 		dest_col.column = std::make_shared<ColumnNullable>(source_col.column);
 		ColumnNullable & nullable_col = static_cast<ColumnNullable &>(*dest_col.column);
-		nullable_col.getNullValuesByteMap() = std::make_shared<ColumnUInt8>(dest_col.column->size());
-		createNullValuesByteMap(block, result);
+		nullable_col.getNullValuesByteMap() = std::make_shared<ColumnUInt8>(dest_col.column->size(), 0);
+		createNullValuesByteMap(block, arguments, result);
 	}
 	else
 		performer(block, arguments, result);