diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index a5027f3..e145083 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -3757,7 +3757,7 @@
     if( operation->id == 0 || !operation->nonce_set )
         return( PSA_ERROR_BAD_STATE );
 
-    if( operation->lengths_set && (operation->ad_remaining != 0 ||
+    if( operation->lengths_set && ( operation->ad_remaining != 0 ||
                                    operation->body_remaining != 0 ) )
         return( PSA_ERROR_INVALID_ARGUMENT );