diff --git a/library/block_cipher.c b/library/block_cipher.c
index bfb605e..e21541e 100644
--- a/library/block_cipher.c
+++ b/library/block_cipher.c
@@ -42,7 +42,7 @@
     }
 }
 
-int mbedtls_cipher_error_from_psa(psa_status_t status)
+static int mbedtls_cipher_error_from_psa(psa_status_t status)
 {
     return PSA_TO_MBEDTLS_ERR_LIST(status, psa_to_cipher_errors,
                                    psa_generic_status_to_mbedtls);