diff --git a/include/polarssl/asn1.h b/include/polarssl/asn1.h
index 0a657e1..c723c00 100644
--- a/include/polarssl/asn1.h
+++ b/include/polarssl/asn1.h
@@ -30,12 +30,12 @@
 #include POLARSSL_CONFIG_FILE
 #endif
 
+#include <stddef.h>
+
 #if defined(POLARSSL_BIGNUM_C)
 #include "bignum.h"
 #endif
 
-#include <string.h>
-
 /**
  * \addtogroup asn1_module
  * \{