diff --git a/include/polarssl/des.h b/include/polarssl/des.h
index b18ca03..3155e5e 100644
--- a/include/polarssl/des.h
+++ b/include/polarssl/des.h
@@ -30,7 +30,7 @@
 #include POLARSSL_CONFIG_FILE
 #endif
 
-#include <string.h>
+#include <stddef.h>
 
 #if defined(_MSC_VER) && !defined(EFIX64) && !defined(EFI32)
 #include <basetsd.h>