diff --git a/library/asn1write.c b/library/asn1write.c
index 8d92888..efdd648 100644
--- a/library/asn1write.c
+++ b/library/asn1write.c
@@ -30,6 +30,8 @@
 
 #include "polarssl/asn1write.h"
 
+#include <string.h>
+
 #if defined(POLARSSL_PLATFORM_C)
 #include "polarssl/platform.h"
 #else