diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 989cfe0..0066744 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -35,6 +35,7 @@
 #include "mbedtls/error.h"
 #include "mbedtls/platform_util.h"
 #include "constant_time.h"
+#include "mbedtls/constant_time.h"
 
 #include <string.h>