diff --git a/library/psa_crypto_mac.c b/library/psa_crypto_mac.c
index d59178e..421d12e 100644
--- a/library/psa_crypto_mac.c
+++ b/library/psa_crypto_mac.c
@@ -236,6 +236,7 @@
     else
 #endif /* BUILTIN_ALG_HMAC */
     {
+        (void) operation;
         status = PSA_ERROR_NOT_SUPPORTED;
     }