diff --git a/client/mifare/mad.h b/client/mifare/mad.h
index ee362adb6..6289982d9 100644
--- a/client/mifare/mad.h
+++ b/client/mifare/mad.h
@@ -13,6 +13,7 @@
 
 #include <stdint.h>
 #include <stdbool.h>
+#include <stddef.h>
 
 typedef struct {
 	uint16_t AID;