diff --git a/auth_algo.cpp b/auth_algo.cpp
index f062b0f..0bc2555 100644
--- a/auth_algo.cpp
+++ b/auth_algo.cpp
@@ -1,5 +1,6 @@
 #include "auth_algo.hpp"
 
+#include <openssl/evp.h>
 #include <openssl/hmac.h>
 #include <openssl/sha.h>