diff --git a/libctru/include/3ds/services/apt.h b/libctru/include/3ds/services/apt.h
index ae961e8..add0bdd 100644
--- a/libctru/include/3ds/services/apt.h
+++ b/libctru/include/3ds/services/apt.h
@@ -139,7 +139,7 @@ void aptSignalReadyForSleep(void);
  * @brief Gets whether to allow the system to enter sleep mode.
  * @return Whether sleep mode is allowed.
  */
-bool aptIsSleepAllowed();
+bool aptIsSleepAllowed(void);
 
 /**
  * @brief Sets whether to allow the system to enter sleep mode.
diff --git a/libctru/source/services/apt.c b/libctru/source/services/apt.c
index 688c16e..1d19167 100644
--- a/libctru/source/services/apt.c
+++ b/libctru/source/services/apt.c
@@ -719,7 +719,7 @@ void aptSignalReadyForSleep(void)
 	svcSignalEvent(aptSleepSync);
 }
 
-bool aptIsSleepAllowed()
+bool aptIsSleepAllowed(void)
 {
 	return aptSleepAllowed;
 }