--- ./src/lib/crypt_ops/crypto_openssl_mgt.h
+++ ./src/lib/crypt_ops/crypto_openssl_mgt.h
@@-16,6 +16,7@@ #include "orconfig.h"
#ifdef ENABLE_OPENSSL
+#include <openssl/engine.h>
#include <openssl/opensslv.h>
/*
Macro to create an arbitrary OpenSSL version number as used by