diff --git a/library/ssl_cli.c b/library/ssl_cli.c
index e0a1c24..3ef318c 100644
--- a/library/ssl_cli.c
+++ b/library/ssl_cli.c
@@ -33,6 +33,7 @@
 #include "ssl_misc.h"
 #include "mbedtls/debug.h"
 #include "mbedtls/error.h"
+#include "constant_time.h"
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
 #include "mbedtls/psa_util.h"