diff --git a/src/lib/drivers/pn531_usb.c b/src/lib/drivers/pn531_usb.c
index e62fb49..2e4a4a3 100644
--- a/src/lib/drivers/pn531_usb.c
+++ b/src/lib/drivers/pn531_usb.c
@@ -25,6 +25,8 @@
 Thanks to d18c7db and Okko for example code
 */
 
+#include <stdlib.h>
+
 #include "../drivers.h"
 #include <nfc/nfc-messages.h>
 
diff --git a/src/lib/drivers/pn533_usb.c b/src/lib/drivers/pn533_usb.c
index 1c9cdad..31ecd3a 100644
--- a/src/lib/drivers/pn533_usb.c
+++ b/src/lib/drivers/pn533_usb.c
@@ -25,6 +25,8 @@
 Thanks to d18c7db and Okko for example code
 */
 
+#include <stdlib.h>
+
 #include "../drivers.h"
 #include <nfc/nfc-messages.h>
 
diff --git a/src/lib/drivers/pn53x_usb.c b/src/lib/drivers/pn53x_usb.c
index 329fb9f..c1eaf14 100644
--- a/src/lib/drivers/pn53x_usb.c
+++ b/src/lib/drivers/pn53x_usb.c
@@ -27,6 +27,7 @@ Thanks to d18c7db and Okko for example code
 
 #include <sys/param.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <usb.h>
 #include <string.h>