diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index ab9ec72..6b01c13 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -1527,7 +1527,7 @@
     psa_key_usage_t usage =
         is_sign ? PSA_KEY_USAGE_SIGN : PSA_KEY_USAGE_VERIFY;
     unsigned char truncated = PSA_MAC_TRUNCATED_LENGTH( alg );
-    psa_algorithm_t full_length_alg = alg & ~PSA_ALG_MAC_TRUNCATION_MASK;
+    psa_algorithm_t full_length_alg = PSA_ALG_FULL_LENGTH_MAC( alg );
 
     status = psa_mac_init( operation, full_length_alg );
     if( status != PSA_SUCCESS )