diff --git a/src/ast/binary_expression.h b/src/ast/binary_expression.h
index 8283a5d..9bce548 100644
--- a/src/ast/binary_expression.h
+++ b/src/ast/binary_expression.h
@@ -127,9 +127,9 @@
  private:
   BinaryExpression(const BinaryExpression&) = delete;
 
-  BinaryOp op_ = BinaryOp::kNone;
-  Expression* lhs_ = nullptr;
-  Expression* rhs_ = nullptr;
+  BinaryOp const op_;
+  Expression* const lhs_;
+  Expression* const rhs_;
 };
 
 inline std::ostream& operator<<(std::ostream& out, BinaryOp op) {