diff --git a/src/curses_output.cc b/src/curses_output.cc
index 27fd4a3..f47b7e6 100644
--- a/src/curses_output.cc
+++ b/src/curses_output.cc
@@ -1,6 +1,6 @@
 #include "curses_output.h"
 
-curses_output::curses_output(std::unique_ptr<cursor> &new_curse):
+curses_output::curses_output(const std::unique_ptr<cursor> &new_curse):
         curse{new_curse} {}
 
 void curses_output::render() {
diff --git a/src/curses_output.h b/src/curses_output.h
index f4b5f3f..51ad948 100644
--- a/src/curses_output.h
+++ b/src/curses_output.h
@@ -8,9 +8,9 @@
 
 class curses_output final : public display {
 private:
-        std::unique_ptr<cursor> &curse;
+        const std::unique_ptr<cursor> &curse;
 public:
-        curses_output(std::unique_ptr<cursor> &new_curse);
+        curses_output(const std::unique_ptr<cursor> &new_curse);
 
         void render() override;
         void clear() override;
diff --git a/src/game.h b/src/game.h
index 9e863c6..03959c8 100644
--- a/src/game.h
+++ b/src/game.h
@@ -13,17 +13,17 @@
 class game final {
 private:
         feature features;
-        std::unique_ptr<input>   &in;
-        std::unique_ptr<display> &out;
-        std::unique_ptr<logger>  &log;
-        std::unique_ptr<RNG>     &rng;
+        const std::unique_ptr<input>   &in;
+        const std::unique_ptr<display> &out;
+        const std::unique_ptr<logger>  &log;
+        const std::unique_ptr<RNG>     &rng;
         std::unique_ptr<character> player;
 public:
         game(const feature enabled_features,
-             std::unique_ptr<input>   &new_in,
-             std::unique_ptr<display> &new_out,
-             std::unique_ptr<logger>  &new_log,
-             std::unique_ptr<RNG>     &new_rng);
+             const std::unique_ptr<input>   &new_in,
+             const std::unique_ptr<display> &new_out,
+             const std::unique_ptr<logger>  &new_log,
+             const std::unique_ptr<RNG>     &new_rng);
         game_status run();
 private:
         int getcmd() const;
diff --git a/src/log.h b/src/log.h
index ccaa105..3b03754 100644
--- a/src/log.h
+++ b/src/log.h
@@ -19,7 +19,7 @@ public:
         void print_char(const position &pos, const char ch);
         void print_str(const position &pos, const std::string &str);
         void print_turn(const unsigned turn);
-        void print_player(std::unique_ptr<character> &player);
+        void print_player(const character &player);
         void print_chlist(const character_list &chlist);
         void print_gold(const gold_list &gold_piles);
         void print_potions(const potion_list &potions);