diff --git a/hardware/arduino/sam/cores/arduino/avr/dtostrf.c b/hardware/arduino/sam/cores/arduino/avr/dtostrf.c
index 51541739c..7f90154fb 100644
--- a/hardware/arduino/sam/cores/arduino/avr/dtostrf.c
+++ b/hardware/arduino/sam/cores/arduino/avr/dtostrf.c
@@ -18,6 +18,8 @@
   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
 
+#include <stdio.h>
+
 char *dtostrf (double val, signed char width, unsigned char prec, char *sout) {
   char fmt[20];
   sprintf(fmt, "%%%d.%df", width, prec);