diff --git a/include/mbedtls/md4.h b/include/mbedtls/md4.h
index f9341a8..ed20370 100644
--- a/include/mbedtls/md4.h
+++ b/include/mbedtls/md4.h
@@ -32,6 +32,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#define MBEDTLS_ERR_MD4_HW_ACCEL_FAILED                   -0x002D  /**< MD4 hardware accelerator failed */
+
 #if ( defined(__ARMCC_VERSION) || defined(_MSC_VER) ) && \
     !defined(inline) && !defined(__cplusplus)
 #define inline __inline