diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 410f648..da6bd61 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1827,7 +1827,7 @@
     else
         psa_mac_abort( operation );
 
-    mbedtls_zeroize( actual_mac, mac_length );
+    mbedtls_zeroize( actual_mac, sizeof( actual_mac ) );
 
     return( status );
 }