diff --git a/Bluetooth.h b/Bluetooth.h
index 8292810..2196070 100644
--- a/Bluetooth.h
+++ b/Bluetooth.h
@@ -11,6 +11,7 @@
 // GNU General Public License for more details.
 
 #pragma once
+#include <Arduino.h>
 
 // You should have received a copy of the GNU General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.