diff --git a/drivers/olimex_iso.c b/drivers/olimex_iso.c
index ef2f9ff..bcbb92c 100644
--- a/drivers/olimex_iso.c
+++ b/drivers/olimex_iso.c
@@ -16,6 +16,7 @@
  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
 
+#include <stdlib.h>
 #include <string.h>
 #include <time.h>