diff --git a/client/mifare/ndef.h b/client/mifare/ndef.h
index 6e79887ee..0aa4cca27 100644
--- a/client/mifare/ndef.h
+++ b/client/mifare/ndef.h
@@ -13,6 +13,7 @@
 
 #include <stdint.h>
 #include <stdbool.h>
+#include <stddef.h>
 
 extern int NDEFDecodeAndPrint(uint8_t *ndef, size_t ndefLen, bool verbose);