diff --git a/include/mbedtls/platform.h b/include/mbedtls/platform.h
index 5cd143c..89fe8a7 100644
--- a/include/mbedtls/platform.h
+++ b/include/mbedtls/platform.h
@@ -43,7 +43,8 @@
 #include "platform_time.h"
 #endif
 
-#define MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED       -0x0070 /**< Hardware accelerator failed */
+#define MBEDTLS_ERR_PLATFORM_HW_ACCEL_FAILED     -0x0070 /**< Hardware accelerator failed */
+#define MBEDTLS_ERR_PLATFORM_FEATURE_UNSUPPORTED -0x0072 /**< The requested feature is not supported by the platform */
 
 #ifdef __cplusplus
 extern "C" {