Prototype update
diff --git a/library/psa_crypto_core.h b/library/psa_crypto_core.h
index 5ea68a6..266b0cc 100644
--- a/library/psa_crypto_core.h
+++ b/library/psa_crypto_core.h
@@ -245,7 +245,7 @@
                                           psa_algorithm_t  alg,
                                           const uint8_t  * hash,
                                           size_t           hash_length,
-                                          uint8_t        * signature,
+                                          const uint8_t  * signature,
                                           size_t           signature_length);
 
 /** Import key data into a slot.