diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index d82ec04..716fa7d 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -34,6 +34,7 @@
 #include "mbedtls/debug.h"
 #include "mbedtls/error.h"
 #include "mbedtls/platform_util.h"
+#include "constant_time.h"
 
 #include <string.h>