diff --git a/src/librustc_trans/cabi_mips64.rs b/src/librustc_trans/cabi_mips64.rs
index e44063faab8105e3160432b67e97c3aea46ea1df..ad35dbeadfc8d375838c4a2e70330b2b9b00fdab 100644
--- a/src/librustc_trans/cabi_mips64.rs
+++ b/src/librustc_trans/cabi_mips64.rs
@@ -8,50 +8,154 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use abi::{ArgType, FnType, LayoutExt, Reg, Uniform};
+use abi::{ArgAttribute, ArgType, CastTarget, FnType, LayoutExt, PassMode, Reg, RegKind, Uniform};
 use context::CodegenCx;
+use rustc::ty::layout::{self, Size};
 
-use rustc::ty::layout::Size;
+fn extend_integer_width_mips(arg: &mut ArgType, bits: u64) {
+    // Always sign extend u32 values on 64-bit mips
+    if let layout::Abi::Scalar(ref scalar) = arg.layout.abi {
+        if let layout::Int(i, signed) = scalar.value {
+            if !signed && i.size().bits() == 32 {
+                if let PassMode::Direct(ref mut attrs) = arg.mode {
+                    attrs.set(ArgAttribute::SExt);
+                    return;
+                }
+            }
+        }
+    }
+
+    arg.extend_integer_width_to(bits);
+}
+
+fn bits_to_int_reg(bits: u64) -> Reg {
+    if bits <= 8 {
+        Reg::i8()
+    } else if bits <= 16 {
+        Reg::i16()
+    } else if bits <= 32 {
+        Reg::i32()
+    } else {
+        Reg::i64()
+    }
+}
 
-fn classify_ret_ty<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>,
-                             ret: &mut ArgType<'tcx>,
-                             offset: &mut Size) {
+fn float_reg<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, ret: &ArgType<'tcx>, i: usize) -> Option<Reg> {
+    match ret.layout.field(cx, i).abi {
+        layout::Abi::Scalar(ref scalar) => match scalar.value {
+            layout::F32 => Some(Reg::f32()),
+            layout::F64 => Some(Reg::f64()),
+            _ => None
+        },
+        _ => None
+    }
+}
+
+fn classify_ret_ty<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, ret: &mut ArgType<'tcx>) {
     if !ret.layout.is_aggregate() {
-        ret.extend_integer_width_to(64);
+        extend_integer_width_mips(ret, 64);
+        return;
+    }
+
+    let size = ret.layout.size;
+    let bits = size.bits();
+    if bits <= 128 {
+        // Unlike other architectures which return aggregates in registers, MIPS n64 limits the
+        // use of float registers to structures (not unions) containing exactly one or two
+        // float fields.
+
+        if let layout::FieldPlacement::Arbitrary { .. } = ret.layout.fields {
+            if ret.layout.fields.count() == 1 {
+                if let Some(reg) = float_reg(cx, ret, 0) {
+                    ret.cast_to(reg);
+                    return;
+                }
+            } else if ret.layout.fields.count() == 2 {
+                if let Some(reg0) = float_reg(cx, ret, 0) {
+                    if let Some(reg1) = float_reg(cx, ret, 1) {
+                        ret.cast_to(CastTarget::Pair(reg0, reg1));
+                        return;
+                    }
+                }
+            }
+        }
+
+        // Cast to a uniform int structure
+        ret.cast_to(Uniform {
+            unit: bits_to_int_reg(bits),
+            total: size
+        });
     } else {
         ret.make_indirect();
-        *offset += cx.tcx.data_layout.pointer_size;
     }
 }
 
-fn classify_arg_ty(cx: &CodegenCx, arg: &mut ArgType, offset: &mut Size) {
+fn classify_arg_ty<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, arg: &mut ArgType<'tcx>) {
+    if !arg.layout.is_aggregate() {
+        extend_integer_width_mips(arg, 64);
+        return;
+    }
+
     let dl = &cx.tcx.data_layout;
     let size = arg.layout.size;
-    let align = arg.layout.align.max(dl.i32_align).min(dl.i64_align);
+    let mut prefix = [RegKind::Integer; 8];
+    let mut prefix_index = 0;
 
-    if arg.layout.is_aggregate() {
-        arg.cast_to(Uniform {
-            unit: Reg::i64(),
-            total: size
-        });
-        if !offset.is_abi_aligned(align) {
-            arg.pad_with(Reg::i64());
+    match arg.layout.fields {
+        layout::FieldPlacement::Array { .. } => {
+            // Arrays are passed indirectly
+            arg.make_indirect();
+            return;
         }
-    } else {
-        arg.extend_integer_width_to(64);
-    }
+        layout::FieldPlacement::Union(_) => {
+            // Unions and are always treated as a series of 64-bit integer chunks
+        },
+        layout::FieldPlacement::Arbitrary { .. } => {
+            // Structures are split up into a series of 64-bit integer chunks, but any aligned
+            // doubles not part of another aggregate are passed as floats.
+            let mut last_offset = Size::from_bytes(0);
+
+            for i in 0..arg.layout.fields.count() {
+                let field = arg.layout.field(cx, i);
+                let offset = arg.layout.fields.offset(i);
+
+                // We only care about aligned doubles
+                if let layout::Abi::Scalar(ref scalar) = field.abi {
+                    if let layout::F64 = scalar.value {
+                        if offset.is_abi_aligned(dl.f64_align) {
+                            // Skip over enough integers to cover [last_offset, offset)
+                            assert!(last_offset.is_abi_aligned(dl.f64_align));
+                            prefix_index += ((offset - last_offset).bits() / 64) as usize;
+
+                            if prefix_index >= prefix.len() {
+                                break;
+                            }
+
+                            prefix[prefix_index] = RegKind::Float;
+                            prefix_index += 1;
+                            last_offset = offset + Reg::f64().size;
+                        }
+                    }
+                }
+            }
+        }
+    };
 
-    *offset = offset.abi_align(align) + size.abi_align(align);
+    // Extract first 8 chunks as the prefix
+    arg.cast_to(CastTarget::ChunkedPrefix {
+        prefix: prefix,
+        chunk: Size::from_bytes(8),
+        total: size
+    });
 }
 
 pub fn compute_abi_info<'a, 'tcx>(cx: &CodegenCx<'a, 'tcx>, fty: &mut FnType<'tcx>) {
-    let mut offset = Size::from_bytes(0);
     if !fty.ret.is_ignore() {
-        classify_ret_ty(cx, &mut fty.ret, &mut offset);
+        classify_ret_ty(cx, &mut fty.ret);
     }
 
     for arg in &mut fty.args {
         if arg.is_ignore() { continue; }
-        classify_arg_ty(cx, arg, &mut offset);
+        classify_arg_ty(cx, arg);
     }
 }