diff --git a/include/polarssl/pbkdf2.h b/include/polarssl/pbkdf2.h
index 0548ad0..7c98eae 100644
--- a/include/polarssl/pbkdf2.h
+++ b/include/polarssl/pbkdf2.h
@@ -27,10 +27,10 @@
 #ifndef POLARSSL_PBKDF2_H
 #define POLARSSL_PBKDF2_H
 
-#include <string.h>
-
 #include "md.h"
 
+#include <stddef.h>
+
 #if defined(_MSC_VER) && !defined(EFIX64) && !defined(EFI32)
 #include <basetsd.h>
 typedef UINT32 uint32_t;