Use a cfg called proc_macro_span to control feature(proc_macro_span)
diff --git a/src/lib.rs b/src/lib.rs
index 374a0bf..306b693 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -80,7 +80,7 @@
// Proc-macro2 types in rustdoc of other crates get linked to here.
#![doc(html_root_url = "https://docs.rs/proc-macro2/0.4.28")]
-#![cfg_attr(all(nightly, not(proc_macro_span_disallowed)), feature(proc_macro_span))]
+#![cfg_attr(any(proc_macro_span, super_unstable), feature(proc_macro_span))]
#![cfg_attr(super_unstable, feature(proc_macro_raw_ident, proc_macro_def_site))]
#[cfg(use_proc_macro)]