diff --git a/authenticator.cpp b/authenticator.cpp
index 6a84b60..9a01f71 100644
--- a/authenticator.cpp
+++ b/authenticator.cpp
@@ -37,7 +37,7 @@ void Authenticator::incFailureCount(std::string ip)
 	fl.lastfail = time(nullptr);
 }
 
-std::vector<char> Authenticator::pbkdf5(std::string password, const std::vector<char> &salt)
+std::vector<char> Authenticator::pbkdf5(std::string password, const std::vector<char> &salt) const
 {
 	unsigned char hash[32];
 	const EVP_MD *sha256 = EVP_sha256();
diff --git a/authenticator.h b/authenticator.h
index b1a450c..8620964 100644
--- a/authenticator.h
+++ b/authenticator.h
@@ -18,7 +18,7 @@ class Authenticator
 	UserDao *userDao;
 	bool isBanned(std::string ip);
 	void incFailureCount(std::string ip);
-	std::vector<char> pbkdf5(std::string password, const std::vector<char> &salt);
+	std::vector<char> pbkdf5(std::string password, const std::vector<char> &salt) const;
 
   public:
 	Authenticator(UserDao &userDao);