diff --git a/src/comp/syntax/codemap.rs b/src/comp/syntax/codemap.rs
index 9725517ed285..8cdbcd32caef 100644
--- a/src/comp/syntax/codemap.rs
+++ b/src/comp/syntax/codemap.rs
@@ -34,12 +34,16 @@ fn next_line(file: filemap, chpos: uint, byte_pos: uint) {
 type lookup_fn = fn(file_pos) -> uint;
 
 fn lookup_pos(map: codemap, pos: uint, lookup: lookup_fn) -> loc {
+    let len = vec::len(map.files);
     let a = 0u;
-    let b = vec::len(map.files);
+    let b = len;
     while b - a > 1u {
         let m = (a + b) / 2u;
         if lookup(map.files[m].start_pos) > pos { b = m; } else { a = m; }
     }
+    if (a >= len) {
+        ret { filename: "-", line: 0u, col: 0u };
+    }
     let f = map.files[a];
     a = 0u;
     b = vec::len(f.lines);
diff --git a/src/comp/syntax/ext/base.rs b/src/comp/syntax/ext/base.rs
index 55294000f66f..798e948a12e8 100644
--- a/src/comp/syntax/ext/base.rs
+++ b/src/comp/syntax/ext/base.rs
@@ -34,9 +34,7 @@ fn syntax_expander_table() -> hashmap<str, syntax_extension> {
 }
 
 obj ext_ctxt(sess: @session,
-             crate_file_name_hack: str,
              mutable backtrace: codemap::opt_span) {
-    fn crate_file_name() -> str { ret crate_file_name_hack; }
 
     fn session() -> @session { ret sess; }
 
@@ -82,16 +80,7 @@ obj ext_ctxt(sess: @session,
 }
 
 fn mk_ctxt(sess: session) -> ext_ctxt {
-    // FIXME: Some extensions work by building ASTs with paths to functions
-    // they need to call at runtime. As those functions live in the std crate,
-    // the paths are prefixed with "std::". Unfortunately, these paths can't
-    // work for code called from inside the stdard library, so here we pass
-    // the extensions the file name of the crate being compiled so they can
-    // use it to guess whether paths should be prepended with "std::". This is
-    // super-ugly and needs a better solution.
-    let crate_file_name_hack = sess.get_codemap().files[0].name;
-
-    ret ext_ctxt(@sess, crate_file_name_hack, codemap::os_none);
+    ret ext_ctxt(@sess, codemap::os_none);
 }
 
 fn expr_to_str(cx: ext_ctxt, expr: @ast::expr, error: str) -> str {
diff --git a/src/comp/syntax/ext/expand.rs b/src/comp/syntax/ext/expand.rs
index ef2105b4271b..150f9ad97bb4 100644
--- a/src/comp/syntax/ext/expand.rs
+++ b/src/comp/syntax/ext/expand.rs
@@ -8,7 +8,7 @@ import vec;
 import syntax::ast::{crate, expr_, expr_mac, mac_invoc};
 import syntax::fold::*;
 import syntax::ext::base::*;
-
+import syntax::parse::parser::parse_expr_from_source_str;
 
 fn expand_expr(exts: hashmap<str, syntax_extension>, cx: ext_ctxt, e: expr_,
                fld: ast_fold, orig: fn@(expr_, ast_fold) -> expr_) -> expr_ {
@@ -47,6 +47,21 @@ fn expand_expr(exts: hashmap<str, syntax_extension>, cx: ext_ctxt, e: expr_,
         };
 }
 
+// FIXME: this is a terrible kludge to inject some macros into the default
+// compilation environment. When the macro-definition system is substantially
+// more mature, these should move from here, into a compiled part of libcore
+// at very least.
+
+fn core_macros() -> str {
+    ret
+"{
+    #macro[[#error[f, ...], log_err #fmt[f, ...]]];
+    #macro[[#warn[f, ...], log_err #fmt[f, ...]]];
+    #macro[[#info[f, ...], log_err #fmt[f, ...]]];
+    #macro[[#debug[f, ...], log_err #fmt[f, ...]]];
+}";
+}
+
 fn expand_crate(sess: session::session, c: @crate) -> @crate {
     let exts = syntax_expander_table();
     let afp = default_ast_fold();
@@ -55,9 +70,16 @@ fn expand_crate(sess: session::session, c: @crate) -> @crate {
         {fold_expr: bind expand_expr(exts, cx, _, _, afp.fold_expr)
             with *afp};
     let f = make_fold(f_pre);
+    let cm = parse_expr_from_source_str("-", core_macros(),
+                                        sess.get_opts().cfg,
+                                        sess.get_parse_sess());
+
+    // This is run for its side-effects on the expander env,
+    // as it registers all the core macros as expanders.
+    f.fold_expr(cm);
+
     let res = @f.fold_crate(*c);
     ret res;
-
 }
 // Local Variables:
 // mode: rust
diff --git a/src/comp/syntax/parse/parser.rs b/src/comp/syntax/parse/parser.rs
index 1b3bb87cddcd..43270de40495 100644
--- a/src/comp/syntax/parse/parser.rs
+++ b/src/comp/syntax/parse/parser.rs
@@ -71,6 +71,16 @@ fn new_parser_from_file(sess: parse_sess, cfg: ast::crate_cfg, path: str,
     ret new_parser(sess, cfg, rdr, ftype);
 }
 
+fn new_parser_from_source_str(sess: parse_sess, cfg: ast::crate_cfg,
+                              name: str, source: str) -> parser {
+    let ftype = SOURCE_FILE;
+    let filemap = codemap::new_filemap(name, 0u, 0u);
+    sess.cm.files += [filemap];
+    let itr = @interner::mk(str::hash, str::eq);
+    let rdr = lexer::new_reader(sess.cm, source, filemap, itr);
+    ret new_parser(sess, cfg, rdr, ftype);
+}
+
 fn new_parser(sess: parse_sess, cfg: ast::crate_cfg, rdr: lexer::reader,
               ftype: file_type) -> parser {
     obj stdio_parser(sess: parse_sess,
@@ -2417,14 +2427,16 @@ fn parse_crate_from_source_file(input: str, cfg: ast::crate_cfg,
     ret parse_crate_mod(p, cfg);
 }
 
+
+fn parse_expr_from_source_str(name: str, source: str, cfg: ast::crate_cfg,
+                              sess: parse_sess) -> @ast::expr {
+    let p = new_parser_from_source_str(sess, cfg, name, source);
+    ret parse_expr(p);
+}
+
 fn parse_crate_from_source_str(name: str, source: str, cfg: ast::crate_cfg,
                                sess: parse_sess) -> @ast::crate {
-    let ftype = SOURCE_FILE;
-    let filemap = codemap::new_filemap(name, 0u, 0u);
-    sess.cm.files += [filemap];
-    let itr = @interner::mk(str::hash, str::eq);
-    let rdr = lexer::new_reader(sess.cm, source, filemap, itr);
-    let p = new_parser(sess, cfg, rdr, ftype);
+    let p = new_parser_from_source_str(sess, cfg, name, source);
     ret parse_crate_mod(p, cfg);
 }