diff --git a/src/graph.c b/src/graph.c
index c26e4e40..f3c043c7 100644
--- a/src/graph.c
+++ b/src/graph.c
@@ -18,6 +18,7 @@
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
+#include <stdlib.h>
 #include "ch.h"
 #include "hal.h"
 #include "gdisp.h"