diff --git a/boot/zephyr/os.c b/boot/zephyr/os.c
index deb9dce..dd0d7e4 100644
--- a/boot/zephyr/os.c
+++ b/boot/zephyr/os.c
@@ -22,7 +22,7 @@
 
 #include "os/os_heap.h"
 
-#ifdef MCUBOOT_USE_MBED_TLS
+#ifdef CONFIG_BOOT_USE_MBEDTLS
 
 #include <mbedtls/platform.h>
 #include <mbedtls/memory_buffer_alloc.h>