diff --git a/library/ssl_cookie.c b/library/ssl_cookie.c
index de0d108..7663e36 100644
--- a/library/ssl_cookie.c
+++ b/library/ssl_cookie.c
@@ -33,6 +33,7 @@
 #if defined(MBEDTLS_SSL_COOKIE_C)
 
 #include "mbedtls/ssl_cookie.h"
+#include "mbedtls/ssl_internal.h"
 
 #if defined(MBEDTLS_PLATFORM_C)
 #include "mbedtls/platform.h"