diff --git a/include/polarssl/error.h b/include/polarssl/error.h
index a084243..728b29e 100644
--- a/include/polarssl/error.h
+++ b/include/polarssl/error.h
@@ -27,6 +27,8 @@
 #ifndef POLARSSL_ERROR_H
 #define POLARSSL_ERROR_H
 
+#include <string.h>
+
 /**
  * Error code layout.
  *