diff --git a/sshaes.c b/sshaes.c
index 759593d7..0b09a6a6 100644
--- a/sshaes.c
+++ b/sshaes.c
@@ -1707,7 +1707,7 @@ static void aes_setup_ni(AESContext * ctx,
 
 #else /* COMPILER_SUPPORTS_AES_NI */
 
-static void aes_setup_ni(AESContext * ctx, unsigned char *key, int keylen)
+static void aes_setup_ni(AESContext * ctx, const unsigned char *key, int keylen)
 {
     assert(0);
 }