diff --git a/cube.h b/cube.h
index 381b140..bd407a9 100644
--- a/cube.h
+++ b/cube.h
@@ -47,6 +47,7 @@
 #include <set>
 #include <unordered_set>
 #include <fstream>
+#include <optional>
 
 #ifdef WIN32
     #define WIN32_LEAN_AND_MEAN
diff --git a/iengine.h b/iengine.h
index d7dd076..17ea7dd 100644
--- a/iengine.h
+++ b/iengine.h
@@ -2145,9 +2145,9 @@ extern int showmat; /**< treat as bool, determines whether material outlines are
  *
  * @param name a C string with the name of the material to look up
  *
- * @return an integer corresponding to the bitmask value of the material
+ * @return an integer corresponding to the bitmask value of the material or std::nullopt if it fails
  */
-extern int findmaterial(const char *name);
+extern std::optional<int> findmaterial(const char *name);
 
 // octaworld
 
diff --git a/slot.h b/slot.h
index f373dad..6819faf 100644
--- a/slot.h
+++ b/slot.h
@@ -112,7 +112,7 @@ struct Slot
 
     virtual VSlot &emptyvslot();
 
-    virtual int cancombine(int type)const;
+    virtual std::optional<int> cancombine(int type) const;
     virtual bool shouldpremul(int) const
     {
         return false;
@@ -122,14 +122,14 @@ struct Slot
      * @brief Attempts to find a tex with index type.
      *
      * Searches for a tex with the type passed, searching only for the part of the
-     * sts vector after `last`. If none is found, returns -1.
+     * sts vector after `last`.
      *
      * @param type the type to seach for
      * @param last the last index to not look at
      *
-     * @return the index where the type was found
+     * @return the index where the type was found, else std::nullopt.
      */
-    int findtextype(int type, int last = -1) const;
+    std::optional<int> findtextype(int type, int last = -1) const;
 
     void load(int index, Slot::Tex &t);
     void load();
@@ -265,7 +265,7 @@ struct DecalSlot final : Slot, VSlot
         return *this;
     }
 
-    int cancombine(int type) const override final;
+    std::optional<int> cancombine(int type) const override final;
     bool shouldpremul(int type) const override final;
 
     void reset()
diff --git a/sound.h b/sound.h
index 582f26b..79376ff 100644
--- a/sound.h
+++ b/sound.h
@@ -52,6 +52,7 @@ class SoundEngine
 
         /**
          * @brief Plays a sound with the given attributes.
+         * 
          *
          * @param n index of the sound to play
          * @param loc world location to play at
@@ -62,8 +63,10 @@ class SoundEngine
          * @param chanid music channel index to use
          * @param radius distance over which sound is audible (in size 0 cubes)
          * @param expire maximum time before the sound stops playing
+         * 
+         * @return the channel id or std::nullopt in case of failure.
          */
-        int playsound(int n, const vec *loc = nullptr, extentity *ent = nullptr, int flags = 0, int loops = 0, int fade = 0, int chanid = -1, int radius = 0, int expire = -1);
+        std::optional<int> playsound(int n, const vec *loc = nullptr, extentity *ent = nullptr, int flags = 0, int loops = 0, int fade = 0, int chanid = -1, int radius = 0, int expire = -1);
 
         /**
          * @brief Stops playing a sound of index n in the specificied channel.
@@ -101,8 +104,10 @@ class SoundEngine
          * @param chanid music channel index to use
          * @param radius distance over which sound is audible (in size 0 cubes)
          * @param expire maximum time before the sound stops playing
+         * 
+         * @return the channel id where the song gets played or std::nullopt if it fails
          */
-        int playsoundname(const char *s, const vec *loc, int vol, int flags, int loops, int fade, int chanid, int radius, int expire);
+        std::optional<int> playsoundname(const char *s, const vec *loc, int vol, int flags, int loops, int fade, int chanid, int radius, int expire);
 
         /**
          * @brief Starts SDL_Mixer and initializes startup sound channels.
@@ -415,7 +420,7 @@ class SoundEngine
             std::vector<SoundConfig> configs;
             const char *dir;
             SoundType(const char *dir, SoundEngine& p);
-            int findsound(const char *name, int vol);
+            std::optional<int> findsound(const char *name, int vol);
             int addslot(const char *name, int vol);
             int addsound(const char *name, int vol, int maxuses = 0);
             void addalt(const char *name, int vol);