diff --git a/include/mbedtls/lms.h b/include/mbedtls/lms.h
index 95fce21..2f29791 100644
--- a/include/mbedtls/lms.h
+++ b/include/mbedtls/lms.h
@@ -364,7 +364,7 @@
 int mbedtls_lms_generate_private_key(mbedtls_lms_private_t *ctx,
                                      mbedtls_lms_algorithm_type_t type,
                                      mbedtls_lmots_algorithm_type_t otstype,
-                                     int (*f_rng)(void *, unsigned char *, size_t),
+                                     mbedtls_f_rng_t *f_rng,
                                      void *p_rng, const unsigned char *seed,
                                      size_t seed_size);
 
@@ -427,7 +427,7 @@
  * \return         A non-zero error code on failure.
  */
 int mbedtls_lms_sign(mbedtls_lms_private_t *ctx,
-                     int (*f_rng)(void *, unsigned char *, size_t),
+                     mbedtls_f_rng_t *f_rng,
                      void *p_rng, const unsigned char *msg,
                      unsigned int msg_size, unsigned char *sig, size_t sig_size,
                      size_t *sig_len);