diff --git a/boot/zephyr/os.c b/boot/zephyr/os.c
index 7c24eb3..1f9b178 100644
--- a/boot/zephyr/os.c
+++ b/boot/zephyr/os.c
@@ -22,9 +22,9 @@
 
 #include "os/os_heap.h"
 
-#if !defined(CONFIG_MBEDTLS) && defined(MCUBOOT_USE_MBED_TLS)
+#ifdef MCUBOOT_USE_MBED_TLS
+#define MBEDTLS_CONFIG_FILE CONFIG_MBEDTLS_CFG_FILE
 
-#define MBEDTLS_CONFIG_FILE MCUBOOT_MBEDTLS_CFG_FILE
 #include <mbedtls/platform.h>
 #include <mbedtls/memory_buffer_alloc.h>
 
@@ -45,6 +45,7 @@
     mbedtls_memory_buffer_alloc_init(mempool, sizeof(mempool));
 }
 #else
+#define MBEDTLS_CONFIG_FILE MCUBOOT_MBEDTLS_CFG_FILE
 void os_heap_init(void)
 {
 }