diff --git a/chacha-sys/cpu-crypt/chacha_cbc.c b/chacha-sys/cpu-crypt/chacha_cbc.c
index c9379eee12..bdee193e32 100644
--- a/chacha-sys/cpu-crypt/chacha_cbc.c
+++ b/chacha-sys/cpu-crypt/chacha_cbc.c
@@ -10,6 +10,7 @@ void chacha20_cbc128_encrypt(const unsigned char* in, unsigned char* out,
 {
     size_t n;
     unsigned char *iv = ivec;
+    (void)key;
 
     if (len == 0) {
         return;