diff --git a/src/librustc/middle/trans/cabi_x86_64.rs b/src/librustc/middle/trans/cabi_x86_64.rs
index 32e481dd2d480..2ab4814fa0cc3 100644
--- a/src/librustc/middle/trans/cabi_x86_64.rs
+++ b/src/librustc/middle/trans/cabi_x86_64.rs
@@ -176,11 +176,15 @@ fn classify_ty(ty: Type) -> Vec<RegClass> {
     }
 
     fn classify_struct(tys: &[Type],
-                       cls: &mut [RegClass], i: uint,
-                       off: uint) {
+                       cls: &mut [RegClass],
+                       i: uint,
+                       off: uint,
+                       packed: bool) {
         let mut field_off = off;
         for ty in tys.iter() {
-            field_off = align(field_off, *ty);
+            if !packed {
+                field_off = align(field_off, *ty);
+            }
             classify(*ty, cls, i, field_off);
             field_off += ty_size(*ty);
         }
@@ -219,7 +223,7 @@ fn classify_ty(ty: Type) -> Vec<RegClass> {
                 unify(cls, ix + off / 8u, SSEDs);
             }
             Struct => {
-                classify_struct(ty.field_types().as_slice(), cls, ix, off);
+                classify_struct(ty.field_types().as_slice(), cls, ix, off, ty.is_packed());
             }
             Array => {
                 let len = ty.array_length();
diff --git a/src/test/run-make/extern-fn-with-packed-struct/Makefile b/src/test/run-make/extern-fn-with-packed-struct/Makefile
new file mode 100644
index 0000000000000..ea6971853fe99
--- /dev/null
+++ b/src/test/run-make/extern-fn-with-packed-struct/Makefile
@@ -0,0 +1,7 @@
+-include ../tools.mk
+
+all:
+	$(CC) -std=c99 test.c -c -o $(TMPDIR)/test.o
+	$(AR) rcs $(TMPDIR)/libtest.a $(TMPDIR)/test.o
+	$(RUSTC) test.rs -L $(TMPDIR)
+	$(call RUN,test) || exit 1
diff --git a/src/test/run-make/extern-fn-with-packed-struct/test.c b/src/test/run-make/extern-fn-with-packed-struct/test.c
new file mode 100644
index 0000000000000..c3456a64b9bc4
--- /dev/null
+++ b/src/test/run-make/extern-fn-with-packed-struct/test.c
@@ -0,0 +1,11 @@
+// Pragma needed cause of gcc bug on windows: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52991
+#pragma pack(1)
+struct __attribute__((packed)) Foo {
+    char a;
+    short b;
+    char c;
+};
+
+struct Foo foo(struct Foo foo) {
+    return foo;
+}
diff --git a/src/test/run-make/extern-fn-with-packed-struct/test.rs b/src/test/run-make/extern-fn-with-packed-struct/test.rs
new file mode 100644
index 0000000000000..4b07b7f39f56d
--- /dev/null
+++ b/src/test/run-make/extern-fn-with-packed-struct/test.rs
@@ -0,0 +1,30 @@
+// 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.
+
+#[packed]
+#[deriving(PartialEq, Show)]
+struct Foo {
+    a: i8,
+    b: i16,
+    c: i8
+}
+
+#[link(name = "test", kind = "static")]
+extern {
+    fn foo(f: Foo) -> Foo;
+}
+
+fn main() {
+    unsafe {
+        let a = Foo { a: 1, b: 2, c: 3 };
+        let b = foo(a);
+        assert_eq!(a, b);
+    }
+}