diff --git a/src/librustsyntax/codemap.rs b/src/librustsyntax/codemap.rs
index e119ae840e6..976a5ee23eb 100644
--- a/src/librustsyntax/codemap.rs
+++ b/src/librustsyntax/codemap.rs
@@ -1,3 +1,5 @@
+import dvec::{dvec, extensions};
+
 export filename;
 export filemap;
 export span;
@@ -42,11 +44,11 @@ type filemap =
     @{name: filename, substr: file_substr, src: @str,
       start_pos: file_pos, mut lines: [file_pos]};
 
-type codemap = @{mut files: [filemap]};
+type codemap = @{files: dvec<filemap>};
 
 type loc = {file: filemap, line: uint, col: uint};
 
-fn new_codemap() -> codemap { @{mut files: [] } }
+fn new_codemap() -> codemap { @{files: dvec()} }
 
 fn new_filemap_w_substr(filename: filename, substr: file_substr,
                         src: @str,
@@ -79,7 +81,7 @@ type lookup_fn = fn@(file_pos) -> uint;
 fn lookup_line(map: codemap, pos: uint, lookup: lookup_fn)
     -> {fm: filemap, line: uint}
 {
-    let len = vec::len(map.files);
+    let len = map.files.len();
     let mut a = 0u;
     let mut b = len;
     while b - a > 1u {
diff --git a/src/librustsyntax/parse.rs b/src/librustsyntax/parse.rs
index a1445e17212..a8000ba4ac0 100644
--- a/src/librustsyntax/parse.rs
+++ b/src/librustsyntax/parse.rs
@@ -1,4 +1,5 @@
 #[doc = "The main parser interface"];
+import dvec::extensions;
 
 export parse_sess;
 export next_node_id;
@@ -152,7 +153,7 @@ fn new_parser_from_source_str(sess: parse_sess, cfg: ast::crate_cfg,
     let ftype = parser::SOURCE_FILE;
     let filemap = codemap::new_filemap_w_substr
         (name, ss, source, sess.chpos, sess.byte_pos);
-    sess.cm.files += [filemap];
+    sess.cm.files.push(filemap);
     let itr = @interner::mk(str::hash, str::eq);
     let rdr = lexer::new_reader(sess.span_diagnostic,
                                 filemap, itr);
@@ -173,7 +174,7 @@ fn new_parser_from_file(sess: parse_sess, cfg: ast::crate_cfg, path: str,
     };
     let filemap = codemap::new_filemap(path, src,
                                        sess.chpos, sess.byte_pos);
-    sess.cm.files += [filemap];
+    sess.cm.files.push(filemap);
     let itr = @interner::mk(str::hash, str::eq);
     let rdr = lexer::new_reader(sess.span_diagnostic, filemap, itr);
     ret new_parser(sess, cfg, rdr, ftype);