Index: src/pbkdf2.h
==================================================================
--- src/pbkdf2.h
+++ src/pbkdf2.h
@@ -33,11 +33,11 @@
 /**
  * @brief The parameters for @ref of_pbkdf2.
  */
 typedef struct of_pbkdf2_parameters_t {
 	/** @brief The HMAC to use to derive a key. */
-	OFHMAC *HMAC;
+	__unsafe_unretained OFHMAC *HMAC;
 	/** @brief The number of iterations to perform. */
 	size_t iterations;
 	/** @brief The salt to derive a key with. */
 	const unsigned char *salt;
 	/** @brief The length of the salt. */