diff --git a/library/sha512.c b/library/sha512.c
index 7530629..7d53731 100644
--- a/library/sha512.c
+++ b/library/sha512.c
@@ -380,7 +380,7 @@
  * SHA-512 final digest
  */
 int mbedtls_sha512_finish_ret( mbedtls_sha512_context *ctx,
-                               unsigned char output[64] )
+                               unsigned char *output )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
     unsigned used;
@@ -453,7 +453,7 @@
  */
 int mbedtls_sha512_ret( const unsigned char *input,
                     size_t ilen,
-                    unsigned char output[64],
+                    unsigned char *output,
                     int is384 )
 {
     int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;