diff --git a/include/polarssl/oid.h b/include/polarssl/oid.h
index 309d8c5..497eac8 100644
--- a/include/polarssl/oid.h
+++ b/include/polarssl/oid.h
@@ -24,14 +24,17 @@
 #ifndef POLARSSL_OID_H
 #define POLARSSL_OID_H
 
-#include <string.h>
 #if !defined(POLARSSL_CONFIG_FILE)
 #include "config.h"
 #else
 #include POLARSSL_CONFIG_FILE
 #endif
+
 #include "asn1.h"
 #include "pk.h"
+
+#include <stddef.h>
+
 #if defined(POLARSSL_CIPHER_C)
 #include "cipher.h"
 #endif