diff --git a/boot/espressif/CMakeLists.txt b/boot/espressif/CMakeLists.txt
index e77eca83b..101034815 100644
--- a/boot/espressif/CMakeLists.txt
+++ b/boot/espressif/CMakeLists.txt
@@ -351,6 +351,7 @@ if(CONFIG_ESP_MCUBOOT_SERIAL)
     list(APPEND port_srcs
         ${CMAKE_CURRENT_LIST_DIR}/port/serial_adapter.c
         ${MBEDTLS_DIR}/library/base64.c
+        ${MBEDTLS_DIR}/library/constant_time.c
         )
     list(APPEND CRYPTO_INC
         ${MBEDTLS_DIR}/include