diff --git a/src/librustc/middle/ty.rs b/src/librustc/middle/ty.rs
index e196304b82ac3..48173cc680428 100644
--- a/src/librustc/middle/ty.rs
+++ b/src/librustc/middle/ty.rs
@@ -2992,14 +2992,13 @@ pub fn lltype_is_sized(cx: &ctxt, ty: t) -> bool {
 pub fn unsized_part_of_type(cx: &ctxt, ty: t) -> t {
     match get(ty).sty {
         ty_str | ty_trait(..) | ty_vec(..) => ty,
-        ty_struct(_, ref substs) => {
-            // Exactly one of the type parameters must be unsized.
-            for tp in substs.types.get_slice(subst::TypeSpace).iter() {
-                if !type_is_sized(cx, *tp) {
-                    return unsized_part_of_type(cx, *tp);
-                }
-            }
-            fail!("Unsized struct type with no unsized type params? {}", ty_to_string(cx, ty));
+        ty_struct(def_id, ref substs) => {
+            let unsized_fields: Vec<_> = struct_fields(cx, def_id, substs).iter()
+                .map(|f| f.mt.ty).filter(|ty| !type_is_sized(cx, *ty)).collect();
+            // Exactly one of the fields must be unsized.
+            assert!(unsized_fields.len() == 1)
+
+            unsized_part_of_type(cx, unsized_fields[0])
         }
         _ => {
             assert!(type_is_sized(cx, ty),
diff --git a/src/test/compile-fail/unsized5.rs b/src/test/compile-fail/unsized5.rs
index 7028f7e798b01..6eecc723431ca 100644
--- a/src/test/compile-fail/unsized5.rs
+++ b/src/test/compile-fail/unsized5.rs
@@ -9,7 +9,7 @@
 // except according to those terms.
 #![feature(struct_variant)]
 
-// Test `Sized?` types not allowed in fields.
+// Test `Sized?` types not allowed in fields (except the last one).
 
 struct S1<Sized? X> {
     f1: X, //~ ERROR type `f1` is dynamically sized. dynamically sized types may only appear as the
@@ -20,7 +20,14 @@ struct S2<Sized? X> {
     g: X, //~ ERROR type `g` is dynamically sized. dynamically sized types may only appear as the ty
     h: int,
 }
-
+struct S3 {
+    f: str, //~ ERROR type `f` is dynamically sized. dynamically sized types may only appear
+    g: [uint]
+}
+struct S4 {
+    f: str, //~ ERROR type `f` is dynamically sized. dynamically sized types may only appear
+    g: uint
+}
 enum E<Sized? X> {
     V1(X, int), //~ERROR type `X` is dynamically sized. dynamically sized types may only appear as t
     V2{f1: X, f: int}, //~ERROR type `f1` is dynamically sized. dynamically sized types may only app
diff --git a/src/test/run-pass/unsized3.rs b/src/test/run-pass/unsized3.rs
new file mode 100644
index 0000000000000..e5e6ce6e76bb6
--- /dev/null
+++ b/src/test/run-pass/unsized3.rs
@@ -0,0 +1,101 @@
+// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Test structs with always-unsized fields.
+
+use std::mem;
+use std::raw;
+
+struct Foo<T> {
+    f: [T],
+}
+
+struct Bar {
+    f1: uint,
+    f2: [uint],
+}
+
+struct Baz {
+    f1: uint,
+    f2: str,
+}
+
+trait Tr {
+    fn foo(&self) -> uint;
+}
+
+struct St {
+    f: uint
+}
+
+impl Tr for St {
+    fn foo(&self) -> uint {
+        self.f
+    }
+}
+
+struct Qux<'a> {
+    f: Tr+'a
+}
+
+pub fn main() {
+    let _: &Foo<f64>;
+    let _: &Bar;
+    let _: &Baz;
+
+    let _: Box<Foo<i32>>;
+    let _: Box<Bar>;
+    let _: Box<Baz>;
+
+    let _ = mem::size_of::<Box<Foo<u8>>>();
+    let _ = mem::size_of::<Box<Bar>>();
+    let _ = mem::size_of::<Box<Baz>>();
+
+    unsafe {
+        struct Foo_<T> {
+            f: [T, ..3]
+        }
+
+        let data = box Foo_{f: [1i32, 2, 3] };
+        let x: &Foo<i32> = mem::transmute(raw::Slice { len: 3, data: &*data });
+        assert!(x.f.len() == 3);
+        assert!(x.f[0] == 1);
+        assert!(x.f[1] == 2);
+        assert!(x.f[2] == 3);
+
+        struct Baz_ {
+            f1: uint,
+            f2: [u8, ..5],
+        }
+
+        let data = box Baz_{ f1: 42, f2: ['a' as u8, 'b' as u8, 'c' as u8, 'd' as u8, 'e' as u8] };
+        let x: &Baz = mem::transmute( raw::Slice { len: 5, data: &*data } );
+        assert!(x.f1 == 42);
+        let chs: Vec<char> = x.f2.chars().collect();
+        assert!(chs.len() == 5);
+        assert!(chs[0] == 'a');
+        assert!(chs[1] == 'b');
+        assert!(chs[2] == 'c');
+        assert!(chs[3] == 'd');
+        assert!(chs[4] == 'e');
+
+        struct Qux_ {
+            f: St
+        }
+
+        let obj: Box<St> = box St { f: 42 };
+        let obj: &Tr = &*obj;
+        let obj: raw::TraitObject = mem::transmute(&*obj);
+        let data = box Qux_{ f: St { f: 234 } };
+        let x: &Qux = mem::transmute(raw::TraitObject { vtable: obj.vtable,
+                                                        data: mem::transmute(&*data) });
+        assert!(x.f.foo() == 234);
+    }
+}