diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index 34b28b1..168f186 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -40,6 +40,7 @@
 #include "mbedtls/error.h"
 #include "mbedtls/platform_util.h"
 #include "mbedtls/version.h"
+#include "constant_time.h"
 
 #include "ssl_invasive.h"