diff --git a/compiler/rustc_builtin_macros/src/derive.rs b/compiler/rustc_builtin_macros/src/derive.rs
index eed7fea11c19c..b5cbfdf0ec6e4 100644
--- a/compiler/rustc_builtin_macros/src/derive.rs
+++ b/compiler/rustc_builtin_macros/src/derive.rs
@@ -167,5 +167,6 @@ fn report_unsafe_args(sess: &Session, meta: &ast::MetaItem) {
             sess.dcx().emit_err(errors::DeriveUnsafePath { span });
         }
         Safety::Default => {}
+        Safety::Safe(_) => unreachable!(),
     }
 }