diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index a4fac64..c7a44f6 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1741,7 +1741,7 @@
                                     size_t hash_length,
                                     const uint8_t *salt,
                                     size_t salt_length,
-                                    uint8_t *signature,
+                                    const uint8_t *signature,
                                     size_t signature_size )
 {
     key_slot_t *slot;