diff --git a/src/libsyntax/ext/source_util.rs b/src/libsyntax/ext/source_util.rs
index fd229d77966..d297188a35c 100644
--- a/src/libsyntax/ext/source_util.rs
+++ b/src/libsyntax/ext/source_util.rs
@@ -197,7 +197,8 @@ pub fn expand_include_bytes(cx: &mut ExtCtxt, sp: Span, tts: &[ast::TokenTree])
 fn res_rel_file(cx: &mut ExtCtxt, sp: codemap::Span, arg: &Path) -> PathBuf {
     // NB: relative paths are resolved relative to the compilation unit
     if !arg.is_absolute() {
-        let mut cu = PathBuf::from(&cx.codemap().span_to_filename(sp));
+        let callsite = cx.codemap().source_callsite(sp);
+        let mut cu = PathBuf::from(&cx.codemap().span_to_filename(callsite));
         cu.pop();
         cu.push(arg);
         cu