diff --git a/sys/arduino/include/serialport.hpp b/sys/arduino/include/serialport.hpp
index c373afbbb30742d3d2d73833e4c604c3c738da94..f9a22ca0fdcfe437a55fc66bad5129a9eea25e48 100644
--- a/sys/arduino/include/serialport.hpp
+++ b/sys/arduino/include/serialport.hpp
@@ -55,7 +55,7 @@ public:
      *
      * @param[in] dev       RIOT UART device
      */
-    SerialPort(uart_t dev);
+    explicit SerialPort(uart_t dev);
 
     /**
      * @brief   Get the number of bytes (characters) available for reading from