diff --git a/libctru/include/3ds/os.h b/libctru/include/3ds/os.h
index fbfebe6..e6d04f9 100644
--- a/libctru/include/3ds/os.h
+++ b/libctru/include/3ds/os.h
@@ -165,7 +165,7 @@ static inline void osTickCounterUpdate(TickCounter* cnt)
  * @param cnt The tick counter.
  * @return The number of milliseconds elapsed.
  */
-double osTickCounterRead(TickCounter* cnt);
+double osTickCounterRead(const TickCounter* cnt);
 
 /**
  * @brief Gets the current Wifi signal strength.
diff --git a/libctru/source/os.c b/libctru/source/os.c
index a54d242..29ad36a 100644
--- a/libctru/source/os.c
+++ b/libctru/source/os.c
@@ -113,7 +113,7 @@ u64 osGetTime(void) {
 }
 
 //---------------------------------------------------------------------------------
-double osTickCounterRead(TickCounter* cnt) {
+double osTickCounterRead(const TickCounter* cnt) {
 //---------------------------------------------------------------------------------
 	return u64_to_double(cnt->elapsed) / CPU_TICKS_PER_MSEC;
 }