SDL_SYS_IsXInputGamepad_DeviceIndex() is only available if SDL_JOYSTICK_XINPUT is true.
diff --git a/src/joystick/SDL_sysjoystick.h b/src/joystick/SDL_sysjoystick.h
index 84efe69..a398695 100644
--- a/src/joystick/SDL_sysjoystick.h
+++ b/src/joystick/SDL_sysjoystick.h
@@ -108,8 +108,10 @@ extern SDL_JoystickGUID SDL_SYS_JoystickGetDeviceGUID(int device_index);
/* Function to return the stable GUID for a opened joystick */
extern SDL_JoystickGUID SDL_SYS_JoystickGetGUID(SDL_Joystick * joystick);
+#if SDL_JOYSTICK_XINPUT
/* Function returns SDL_TRUE if this device is an XInput gamepad */
extern SDL_bool SDL_SYS_IsXInputGamepad_DeviceIndex(int device_index);
+#endif
#endif /* _SDL_sysjoystick_h */