diff --git a/src/comp/back/link.rs b/src/comp/back/link.rs
index 3805f937c9d..29eb74e41eb 100644
--- a/src/comp/back/link.rs
+++ b/src/comp/back/link.rs
@@ -40,7 +40,9 @@ fn llvm_err(sess: session::session, msg: str) {
 }
 
 fn link_intrinsics(sess: session::session, llmod: ModuleRef) {
-    let path = fs::connect(sess.get_opts().sysroot, "lib/intrinsics.bc");
+    let path = istr::to_estr(
+        fs::connect(istr::from_estr(sess.get_opts().sysroot),
+                    ~"lib/intrinsics.bc"));
     let membuf =
         llvm::LLVMRustCreateMemoryBufferWithContentsOfFile(str::buf(path));
     if membuf as uint == 0u {
@@ -360,10 +362,12 @@ fn build_link_meta(sess: &session::session, c: &ast::crate, output: &str,
               none. {
                 let name =
                     {
-                        let os = str::split(fs::basename(output), '.' as u8);
+                        let os = istr::split(
+                            fs::basename(istr::from_estr(output)),
+                            '.' as u8);
                         assert (vec::len(os) >= 2u);
                         vec::pop(os);
-                        str::connect(os, ".")
+                        istr::to_estr(istr::connect(os, ~"."))
                     };
                 warn_missing(sess, "name", name);
                 name
diff --git a/src/comp/driver/rustc.rs b/src/comp/driver/rustc.rs
index 918fc05fb25..c65ecfaaf2a 100644
--- a/src/comp/driver/rustc.rs
+++ b/src/comp/driver/rustc.rs
@@ -312,7 +312,8 @@ fn get_arch(triple: str) -> session::arch {
 }
 
 fn get_default_sysroot(binary: str) -> str {
-    let dirname = fs::dirname(binary);
+    let dirname = istr::to_estr(
+        fs::dirname(istr::from_estr(binary)));
     if str::eq(dirname, binary) { ret "."; }
     ret dirname;
 }
@@ -443,7 +444,8 @@ fn opts() -> [getopts::opt] {
 
 fn main(args: [str]) {
     let binary = vec::shift(args);
-    let binary_dir = fs::dirname(binary);
+    let binary_dir = istr::to_estr(
+        fs::dirname(istr::from_estr(binary)));
     let match =
         alt getopts::getopts(args, opts()) {
           getopts::success(m) { m }
@@ -557,20 +559,20 @@ fn main(args: [str]) {
     } else { lib_cmd = "-shared"; }
 
     // Converts a library file name into a gcc -l argument
-    fn unlib(config: @session::config, filename: str) -> str {
+    fn unlib(config: @session::config, filename: &istr) -> istr {
         let rmlib =
-            bind fn (config: @session::config, filename: str) -> str {
-                     if config.os == session::os_macos ||
-                            config.os == session::os_linux &&
-                                str::find(filename, "lib") == 0 {
-                         ret str::slice(filename, 3u,
-                                        str::byte_len(filename));
-                     } else { ret filename; }
-                 }(config, _);
-        fn rmext(filename: str) -> str {
-            let parts = str::split(filename, '.' as u8);
+            bind fn (config: @session::config, filename: &istr) -> istr {
+            if config.os == session::os_macos ||
+                config.os == session::os_linux &&
+                istr::find(filename, ~"lib") == 0 {
+                ret istr::slice(filename, 3u,
+                                istr::byte_len(filename));
+            } else { ret filename; }
+        }(config, _);
+        fn rmext(filename: &istr) -> istr {
+            let parts = istr::split(filename, '.' as u8);
             vec::pop(parts);
-            ret str::connect(parts, ".");
+            ret istr::connect(parts, ~".");
         }
         ret alt config.os {
               session::os_macos. { rmext(rmlib(filename)) }
@@ -585,10 +587,11 @@ fn main(args: [str]) {
             gcc_args += [cratepath];
             cont;
         }
+        let cratepath = istr::from_estr(cratepath);
         let dir = fs::dirname(cratepath);
-        if dir != "" { gcc_args += ["-L" + dir]; }
+        if dir != ~"" { gcc_args += ["-L" + istr::to_estr(dir)]; }
         let libarg = unlib(sess.get_targ_cfg(), fs::basename(cratepath));
-        gcc_args += ["-l" + libarg];
+        gcc_args += ["-l" + istr::to_estr(libarg)];
     }
 
     let ula = cstore::get_used_link_args(cstore);
diff --git a/src/comp/metadata/creader.rs b/src/comp/metadata/creader.rs
index b2570e41148..c13de2d6f9d 100644
--- a/src/comp/metadata/creader.rs
+++ b/src/comp/metadata/creader.rs
@@ -15,6 +15,7 @@ import back::x86;
 import util::common;
 import std::vec;
 import std::str;
+import std::istr;
 import std::fs;
 import std::io;
 import std::option;
@@ -150,7 +151,8 @@ fn find_library_crate_aux(nn: &{prefix: str, suffix: str}, crate_name: str,
                           metas: &[@ast::meta_item],
                           library_search_paths: &[str]) ->
    option::t<{ident: str, data: @[u8]}> {
-    let prefix: str = nn.prefix + crate_name;
+    let prefix: istr = istr::from_estr(nn.prefix + crate_name);
+    let suffix: istr = istr::from_estr(nn.suffix);
     // FIXME: we could probably use a 'glob' function in std::fs but it will
     // be much easier to write once the unsafe module knows more about FFI
     // tricks. Currently the glob(3) interface is a bit more than we can
@@ -159,13 +161,17 @@ fn find_library_crate_aux(nn: &{prefix: str, suffix: str}, crate_name: str,
 
     for library_search_path: str in library_search_paths {
         log #fmt["searching %s", library_search_path];
-        for path: str in fs::list_dir(library_search_path) {
-            log #fmt["searching %s", path];
-            let f: str = fs::basename(path);
-            if !(str::starts_with(f, prefix) && str::ends_with(f, nn.suffix))
+        let library_search_path = istr::from_estr(library_search_path);
+        for path: istr in fs::list_dir(library_search_path) {
+            log #fmt["searching %s", istr::to_estr(path)];
+            let f: istr = fs::basename(path);
+            let path = istr::to_estr(path);
+            if !(istr::starts_with(f, prefix) && istr::ends_with(f, suffix))
                {
-                log #fmt["skipping %s, doesn't look like %s*%s", path, prefix,
-                         nn.suffix];
+                log #fmt["skipping %s, doesn't look like %s*%s",
+                         path,
+                         istr::to_estr(prefix),
+                         istr::to_estr(suffix)];
                 cont;
             }
             alt get_metadata_section(path) {
diff --git a/src/comp/syntax/parse/eval.rs b/src/comp/syntax/parse/eval.rs
index af1ba91b37b..18d9a04ebbf 100644
--- a/src/comp/syntax/parse/eval.rs
+++ b/src/comp/syntax/parse/eval.rs
@@ -1,5 +1,6 @@
 
 import std::str;
+import std::istr;
 import std::option;
 import std::option::some;
 import std::option::none;
@@ -48,10 +49,12 @@ fn eval_crate_directive(cx: ctx, cdir: @ast::crate_directive, prefix: str,
       ast::cdir_src_mod(id, file_opt, attrs) {
         let file_path = id + ".rs";
         alt file_opt { some(f) { file_path = f; } none. { } }
-        let full_path =
-            if std::fs::path_is_absolute(file_path) {
-                file_path
-            } else { prefix + std::fs::path_sep() + file_path };
+        let full_path = if std::fs::path_is_absolute(
+            istr::from_estr(file_path)) {
+            file_path
+        } else {
+            prefix + istr::to_estr(std::fs::path_sep()) + file_path
+        };
         if cx.mode == mode_depend { cx.deps += [full_path]; ret; }
         let p0 =
             new_parser_from_file(cx.sess, cx.cfg, full_path, cx.chpos,
@@ -73,9 +76,9 @@ fn eval_crate_directive(cx: ctx, cdir: @ast::crate_directive, prefix: str,
         let path = id;
         alt dir_opt { some(d) { path = d; } none. { } }
         let full_path =
-            if std::fs::path_is_absolute(path) {
+            if std::fs::path_is_absolute(istr::from_estr(path)) {
                 path
-            } else { prefix + std::fs::path_sep() + path };
+            } else { prefix + istr::to_estr(std::fs::path_sep()) + path };
         let m0 = eval_crate_directives_to_mod(cx, cdirs, full_path);
         let i =
             @{ident: id,
diff --git a/src/comp/syntax/parse/parser.rs b/src/comp/syntax/parse/parser.rs
index 8ee2645fe5d..59cea6e131d 100644
--- a/src/comp/syntax/parse/parser.rs
+++ b/src/comp/syntax/parse/parser.rs
@@ -2,6 +2,7 @@
 import std::io;
 import std::vec;
 import std::str;
+import std::istr;
 import std::option;
 import std::option::some;
 import std::option::none;
@@ -2525,7 +2526,8 @@ fn parse_crate_from_crate_file(input: &str, cfg: &ast::crate_cfg,
                                sess: &parse_sess) -> @ast::crate {
     let p = new_parser_from_file(sess, cfg, input, 0u, 0u, CRATE_FILE);
     let lo = p.get_lo_pos();
-    let prefix = std::fs::dirname(p.get_filemap().name);
+    let prefix = istr::to_estr(
+        std::fs::dirname(istr::from_estr(p.get_filemap().name)));
     let leading_attrs = parse_inner_attrs_and_next(p);
     let crate_attrs = leading_attrs.inner;
     let first_cdir_attr = leading_attrs.next;
diff --git a/src/fuzzer/fuzzer.rs b/src/fuzzer/fuzzer.rs
index d9c3f979e39..3f88f26bdcd 100644
--- a/src/fuzzer/fuzzer.rs
+++ b/src/fuzzer/fuzzer.rs
@@ -10,6 +10,7 @@ import std::io;
 import std::io::stdout;
 import std::vec;
 import std::str;
+import std::istr;
 import std::uint;
 import std::option;
 
@@ -40,8 +41,11 @@ fn find_rust_files(files: &mutable [str], path: str) {
         if file_contains(path, "xfail-stage1") {
             //log_err "Skipping " + path + " because it is marked as xfail-stage1";
         } else { files += [path]; }
-    } else if fs::file_is_dir(path) && str::find(path, "compile-fail") == -1 {
-        for p in fs::list_dir(path) { find_rust_files(files, p); }
+    } else if fs::file_is_dir(istr::from_estr(path))
+        && str::find(path, "compile-fail") == -1 {
+        for p in fs::list_dir(istr::from_estr(path)) {
+            find_rust_files(files, istr::to_estr(p));
+        }
     }
 }
 
diff --git a/src/lib/fs.rs b/src/lib/fs.rs
index c49d77815a3..9bf6d40323f 100644
--- a/src/lib/fs.rs
+++ b/src/lib/fs.rs
@@ -7,34 +7,34 @@ native "rust" mod rustrt {
     fn rust_file_is_dir(path: str) -> int;
 }
 
-fn path_sep() -> str { ret str::from_char(os_fs::path_sep); }
+fn path_sep() -> istr { ret istr::from_char(os_fs::path_sep); }
 
-type path = str;
+type path = istr;
 
-fn dirname(p: path) -> path {
-    let i: int = str::rindex(p, os_fs::path_sep as u8);
+fn dirname(p: &path) -> path {
+    let i: int = istr::rindex(p, os_fs::path_sep as u8);
     if i == -1 {
-        i = str::rindex(p, os_fs::alt_path_sep as u8);
-        if i == -1 { ret "."; }
+        i = istr::rindex(p, os_fs::alt_path_sep as u8);
+        if i == -1 { ret ~"."; }
     }
-    ret str::substr(p, 0u, i as uint);
+    ret istr::substr(p, 0u, i as uint);
 }
 
-fn basename(p: path) -> path {
-    let i: int = str::rindex(p, os_fs::path_sep as u8);
+fn basename(p: &path) -> path {
+    let i: int = istr::rindex(p, os_fs::path_sep as u8);
     if i == -1 {
-        i = str::rindex(p, os_fs::alt_path_sep as u8);
+        i = istr::rindex(p, os_fs::alt_path_sep as u8);
         if i == -1 { ret p; }
     }
-    let len = str::byte_len(p);
+    let len = istr::byte_len(p);
     if i + 1 as uint >= len { ret p; }
-    ret str::slice(p, i + 1 as uint, len);
+    ret istr::slice(p, i + 1 as uint, len);
 }
 
 
 // FIXME: Need some typestate to avoid bounds check when len(pre) == 0
-fn connect(pre: path, post: path) -> path {
-    let len = str::byte_len(pre);
+fn connect(pre: &path, post: &path) -> path {
+    let len = istr::byte_len(pre);
     ret if pre[len - 1u] == os_fs::path_sep as u8 {
 
             // Trailing '/'?
@@ -42,26 +42,36 @@ fn connect(pre: path, post: path) -> path {
         } else { pre + path_sep() + post };
 }
 
-fn file_is_dir(p: path) -> bool { ret rustrt::rust_file_is_dir(p) != 0; }
+fn file_is_dir(p: &path) -> bool {
+    ret rustrt::rust_file_is_dir(istr::to_estr(p)) != 0;
+}
 
-fn list_dir(p: path) -> [str] {
-    let pl = str::byte_len(p);
+fn list_dir(p: &path) -> [istr] {
+    let p = p;
+    let pl = istr::byte_len(p);
     if pl == 0u || p[pl - 1u] as char != os_fs::path_sep { p += path_sep(); }
-    let full_paths: [str] = [];
-    for filename: str in os_fs::list_dir(p) {
-        if !str::eq(filename, ".") {
-            if !str::eq(filename, "..") { full_paths += [p + filename]; }
+    let full_paths: [istr] = [];
+    for filename: str in os_fs::list_dir(istr::to_estr(p)) {
+        let filename = istr::from_estr(filename);
+        if !istr::eq(filename, ~".") {
+            if !istr::eq(filename, ~"..") { full_paths += [p + filename]; }
         }
     }
     ret full_paths;
 }
 
-fn path_is_absolute(p: path) -> bool { ret os_fs::path_is_absolute(p); }
+fn path_is_absolute(p: &path) -> bool {
+    ret os_fs::path_is_absolute(istr::to_estr(p));
+}
 
 // FIXME: under Windows, we should prepend the current drive letter to paths
 // that start with a slash.
-fn make_absolute(p: path) -> path {
-    if path_is_absolute(p) { ret p; } else { ret connect(getcwd(), p); }
+fn make_absolute(p: &path) -> path {
+    if path_is_absolute(p) {
+        ret p;
+    } else {
+        ret connect(istr::from_estr(getcwd()), p);
+    }
 }
 
 // Local Variables:
diff --git a/src/lib/istr.rs b/src/lib/istr.rs
index 1556065e087..9e1fa37693d 100644
--- a/src/lib/istr.rs
+++ b/src/lib/istr.rs
@@ -3,7 +3,7 @@ index, rindex, find, starts_with, ends_with, substr, slice, split,
 concat, connect, to_upper, replace, char_slice, trim_left, trim_right, trim,
 unshift_char, shift_char, pop_char, push_char, is_utf8, from_chars, to_chars,
 char_len, char_at, bytes, is_ascii, shift_byte, pop_byte, unsafe_from_byte,
-unsafe_from_bytes;
+unsafe_from_bytes, from_char;
 
 export from_estr, to_estr;
 
diff --git a/src/test/compiletest/compiletest.rs b/src/test/compiletest/compiletest.rs
index 778ade3ce64..af4ae5c85cd 100644
--- a/src/test/compiletest/compiletest.rs
+++ b/src/test/compiletest/compiletest.rs
@@ -3,6 +3,7 @@ import std::getopts;
 import std::test;
 import std::fs;
 import std::str;
+import std::istr;
 import std::vec;
 import std::task;
 
@@ -126,7 +127,8 @@ fn make_tests(cx: &cx) -> tests_and_conv_fn {
     log #fmt["making tests from %s", cx.config.src_base];
     let configport = port::<[u8]>();
     let tests = [];
-    for file: str in fs::list_dir(cx.config.src_base) {
+    for file: istr in fs::list_dir(istr::from_estr(cx.config.src_base)) {
+        let file = istr::to_estr(file);
         log #fmt["inspecting file %s", file];
         if is_test(cx.config, file) {
             tests += [make_test(cx, file, configport)];
@@ -137,19 +139,21 @@ fn make_tests(cx: &cx) -> tests_and_conv_fn {
 
 fn is_test(config: &config, testfile: &str) -> bool {
     // Pretty-printer does not work with .rc files yet
-    let valid_extensions =
-        alt config.mode { mode_pretty. { [".rs"] } _ { [".rc", ".rs"] } };
-    let invalid_prefixes = [".", "#", "~"];
-    let name = fs::basename(testfile);
+    let valid_extensions = alt config.mode {
+      mode_pretty. { [~".rs"] }
+      _ { [~".rc", ~".rs"] }
+    };
+    let invalid_prefixes = [~".", ~"#", ~"~"];
+    let name = fs::basename(istr::from_estr(testfile));
 
     let valid = false;
 
     for ext in valid_extensions {
-        if str::ends_with(name, ext) { valid = true }
+        if istr::ends_with(name, ext) { valid = true }
     }
 
     for pre in invalid_prefixes {
-        if str::starts_with(name, pre) { valid = false }
+        if istr::starts_with(name, pre) { valid = false }
     }
 
     ret valid;
diff --git a/src/test/compiletest/header.rs b/src/test/compiletest/header.rs
index 631de4008da..209787c78f4 100644
--- a/src/test/compiletest/header.rs
+++ b/src/test/compiletest/header.rs
@@ -1,5 +1,6 @@
 import std::option;
 import std::str;
+import std::istr;
 import std::io;
 import std::fs;
 
@@ -95,7 +96,8 @@ fn parse_pp_exact(line: &str, testfile: &str) -> option::t<str> {
       option::some(s) { option::some(s) }
       option::none. {
         if parse_name_directive(line, "pp-exact") {
-            option::some(fs::basename(testfile))
+            option::some(istr::to_estr(
+                fs::basename(istr::from_estr(testfile))))
         } else {
             option::none
         }
diff --git a/src/test/compiletest/runtest.rs b/src/test/compiletest/runtest.rs
index 17ee810e604..ca9c02fb1be 100644
--- a/src/test/compiletest/runtest.rs
+++ b/src/test/compiletest/runtest.rs
@@ -1,5 +1,6 @@
 import std::io;
 import std::str;
+import std::istr;
 import std::option;
 import std::fs;
 import std::os;
@@ -105,8 +106,9 @@ fn run_pretty_test(cx: &cx, props: &test_props, testfile: &str) {
     let expected =
         alt props.pp_exact {
           option::some(file) {
-            let filepath = fs::connect(fs::dirname(testfile), file);
-            io::read_whole_file_str(filepath)
+            let filepath = fs::connect(fs::dirname(
+                istr::from_estr(testfile)), istr::from_estr(file));
+            io::read_whole_file_str(istr::to_estr(filepath))
           }
           option::none. { srcs[vec::len(srcs) - 2u] }
         };
@@ -338,11 +340,12 @@ fn output_base_name(config: &config, testfile: &str) -> str {
     let base = config.build_base;
     let filename =
         {
-            let parts = str::split(fs::basename(testfile), '.' as u8);
+            let parts = istr::split(fs::basename(istr::from_estr(testfile)),
+                                    '.' as u8);
             parts = vec::slice(parts, 0u, vec::len(parts) - 1u);
-            str::connect(parts, ".")
+            istr::connect(parts, ~".")
         };
-    #fmt["%s%s.%s", base, filename, config.stage_id]
+    #fmt["%s%s.%s", base, istr::to_estr(filename), config.stage_id]
 }
 
 fn maybe_dump_to_stdout(config: &config, out: &str, err: &str) {
diff --git a/src/test/stdtest/fs.rs b/src/test/stdtest/fs.rs
index 7c33b37e4ef..be920418e16 100644
--- a/src/test/stdtest/fs.rs
+++ b/src/test/stdtest/fs.rs
@@ -5,12 +5,12 @@ import std::fs;
 #[test]
 fn test_connect() {
     let slash = fs::path_sep();
-    log_err fs::connect("a", "b");
-    assert (fs::connect("a", "b") == "a" + slash + "b");
-    assert (fs::connect("a" + slash, "b") == "a" + slash + "b");
+    log_err fs::connect(~"a", ~"b");
+    assert (fs::connect(~"a", ~"b") == ~"a" + slash + ~"b");
+    assert (fs::connect(~"a" + slash, ~"b") == ~"a" + slash + ~"b");
 }
 
 // Issue #712
 #[test]
-fn test_list_dir_no_invalid_memory_access() { fs::list_dir("."); }
+fn test_list_dir_no_invalid_memory_access() { fs::list_dir(~"."); }
 
diff --git a/src/test/stdtest/path.rs b/src/test/stdtest/path.rs
index 911bc6b0dd9..147e9b29eec 100644
--- a/src/test/stdtest/path.rs
+++ b/src/test/stdtest/path.rs
@@ -8,10 +8,10 @@ import std::os;
 
 #[test]
 fn test() {
-    assert (!fs::path_is_absolute("test-path"));
+    assert (!fs::path_is_absolute(~"test-path"));
 
     log "Current working directory: " + os::getcwd();
 
-    log fs::make_absolute("test-path");
-    log fs::make_absolute("/usr/bin");
+    log fs::make_absolute(~"test-path");
+    log fs::make_absolute(~"/usr/bin");
 }