diff --git a/src/include/storage/page/b_plus_tree_internal_page.h b/src/include/storage/page/b_plus_tree_internal_page.h
index 54e8748c3..7f18442e0 100644
--- a/src/include/storage/page/b_plus_tree_internal_page.h
+++ b/src/include/storage/page/b_plus_tree_internal_page.h
@@ -52,7 +52,7 @@ class BPlusTreeInternalPage : public BPlusTreePage {
 
   void Init(int max_size = INTERNAL_PAGE_SLOT_CNT);
 
-  auto KeyAt(int index) const -> KeyType;
+  auto KeyAt(int index) const -> const KeyType &;
 
   void SetKeyAt(int index, const KeyType &key);
 
@@ -62,7 +62,7 @@ class BPlusTreeInternalPage : public BPlusTreePage {
    */
   auto ValueIndex(const ValueType &value) const -> int;
 
-  auto ValueAt(int index) const -> ValueType;
+  auto ValueAt(int index) const -> const ValueType &;
 
   /**
    * @brief For test only, return a string representing all keys in
diff --git a/src/include/storage/page/b_plus_tree_leaf_page.h b/src/include/storage/page/b_plus_tree_leaf_page.h
index 6915aa809..3024ad3ef 100644
--- a/src/include/storage/page/b_plus_tree_leaf_page.h
+++ b/src/include/storage/page/b_plus_tree_leaf_page.h
@@ -60,7 +60,7 @@ class BPlusTreeLeafPage : public BPlusTreePage {
   // Helper methods
   auto GetNextPageId() const -> page_id_t;
   void SetNextPageId(page_id_t next_page_id);
-  auto KeyAt(int index) const -> KeyType;
+  auto KeyAt(int index) const -> const KeyType &;
 
   /**
    * @brief For test only return a string representing all keys in
diff --git a/src/storage/page/b_plus_tree_internal_page.cpp b/src/storage/page/b_plus_tree_internal_page.cpp
index 0e72857ec..85b8588e9 100644
--- a/src/storage/page/b_plus_tree_internal_page.cpp
+++ b/src/storage/page/b_plus_tree_internal_page.cpp
@@ -41,7 +41,7 @@ void B_PLUS_TREE_INTERNAL_PAGE_TYPE::Init(int max_size) { UNIMPLEMENTED("TODO(P2
  * @return Key at index
  */
 INDEX_TEMPLATE_ARGUMENTS
-auto B_PLUS_TREE_INTERNAL_PAGE_TYPE::KeyAt(int index) const -> KeyType {
+auto B_PLUS_TREE_INTERNAL_PAGE_TYPE::KeyAt(int index) const -> const KeyType & {
   UNIMPLEMENTED("TODO(P2): Add implementation.");
 }
 
@@ -64,7 +64,7 @@ void B_PLUS_TREE_INTERNAL_PAGE_TYPE::SetKeyAt(int index, const KeyType &key) {
  * @return Value at index
  */
 INDEX_TEMPLATE_ARGUMENTS
-auto B_PLUS_TREE_INTERNAL_PAGE_TYPE::ValueAt(int index) const -> ValueType {
+auto B_PLUS_TREE_INTERNAL_PAGE_TYPE::ValueAt(int index) const -> const ValueType & {
   UNIMPLEMENTED("TODO(P2): Add implementation.");
 }
 
diff --git a/src/storage/page/b_plus_tree_leaf_page.cpp b/src/storage/page/b_plus_tree_leaf_page.cpp
index 3199994ef..f7d694676 100644
--- a/src/storage/page/b_plus_tree_leaf_page.cpp
+++ b/src/storage/page/b_plus_tree_leaf_page.cpp
@@ -50,7 +50,9 @@ void B_PLUS_TREE_LEAF_PAGE_TYPE::SetNextPageId(page_id_t next_page_id) {
  * array offset)
  */
 INDEX_TEMPLATE_ARGUMENTS
-auto B_PLUS_TREE_LEAF_PAGE_TYPE::KeyAt(int index) const -> KeyType { UNIMPLEMENTED("TODO(P2): Add implementation."); }
+auto B_PLUS_TREE_LEAF_PAGE_TYPE::KeyAt(int index) const -> const KeyType & {
+  UNIMPLEMENTED("TODO(P2): Add implementation.");
+}
 
 template class BPlusTreeLeafPage<GenericKey<4>, RID, GenericComparator<4>>;
 template class BPlusTreeLeafPage<GenericKey<8>, RID, GenericComparator<8>>;