diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index 79348bd8dd..a1a5859f05 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -3198,7 +3198,7 @@ static void ssl_calc_finished_tls_sha256(
 
 #if defined(MBEDTLS_SHA512_C)
 
-typedef int (*finish_sha384_t)(mbedtls_sha512_context*, unsigned char[48]);
+typedef int (*finish_sha384_t)(mbedtls_sha512_context*, unsigned char*);
 
 static void ssl_calc_finished_tls_sha384(
                 mbedtls_ssl_context *ssl, unsigned char *buf, int from )