Use a cfg called proc_macro_span to control feature(proc_macro_span)
diff --git a/src/wrapper.rs b/src/wrapper.rs
index cbb6515..8413eaa 100644
--- a/src/wrapper.rs
+++ b/src/wrapper.rs
@@ -478,12 +478,12 @@
     #[cfg(any(super_unstable, feature = "span-locations"))]
     pub fn start(&self) -> LineColumn {
         match self {
-            #[cfg(nightly)]
+            #[cfg(proc_macro_span)]
             Span::Compiler(s) => {
                 let proc_macro::LineColumn { line, column } = s.start();
                 LineColumn { line, column }
             }
-            #[cfg(not(nightly))]
+            #[cfg(not(proc_macro_span))]
             Span::Compiler(_) => LineColumn { line: 0, column: 0 },
             Span::Fallback(s) => {
                 let fallback::LineColumn { line, column } = s.start();
@@ -495,12 +495,12 @@
     #[cfg(any(super_unstable, feature = "span-locations"))]
     pub fn end(&self) -> LineColumn {
         match self {
-            #[cfg(nightly)]
+            #[cfg(proc_macro_span)]
             Span::Compiler(s) => {
                 let proc_macro::LineColumn { line, column } = s.end();
                 LineColumn { line, column }
             }
-            #[cfg(not(nightly))]
+            #[cfg(not(proc_macro_span))]
             Span::Compiler(_) => LineColumn { line: 0, column: 0 },
             Span::Fallback(s) => {
                 let fallback::LineColumn { line, column } = s.end();