diff --git a/src/cpp/benders/outer_loop/OuterLoopInputDataReader.cpp b/src/cpp/benders/outer_loop/OuterLoopInputDataReader.cpp
index 889301284..94a01074a 100644
--- a/src/cpp/benders/outer_loop/OuterLoopInputDataReader.cpp
+++ b/src/cpp/benders/outer_loop/OuterLoopInputDataReader.cpp
@@ -53,7 +53,7 @@ void OuterLoopInputData::AddSingleData(const OuterLoopSingleInputData &data) {
   outer_loop_data_.push_back(data);
 }
 
-std::vector<OuterLoopSingleInputData> OuterLoopInputData::OuterLoopData()
+const std::vector<OuterLoopSingleInputData> &OuterLoopInputData::OuterLoopData()
     const {
   return outer_loop_data_;
 }
diff --git a/src/cpp/benders/outer_loop/include/OuterLoopInputDataReader.h b/src/cpp/benders/outer_loop/include/OuterLoopInputDataReader.h
index 0c40875d7..ef31a46b6 100644
--- a/src/cpp/benders/outer_loop/include/OuterLoopInputDataReader.h
+++ b/src/cpp/benders/outer_loop/include/OuterLoopInputDataReader.h
@@ -80,7 +80,8 @@ class OuterLoopInputData {
  public:
   OuterLoopInputData() = default;
 
-  [[nodiscard]] std::vector<OuterLoopSingleInputData> OuterLoopData() const;
+  [[nodiscard]] const std::vector<OuterLoopSingleInputData> &OuterLoopData()
+      const;
   [[nodiscard]] std::vector<std::string> PatternBodies() const;
   [[nodiscard]] std::string PatternsPrefix() const;